A000016 -id:A000016 - cp's OEIS frontend

A307683 Number of partitions of n having a non-integer median.

0, 0, 1, 0, 2, 1, 4, 1, 7, 5, 11, 8, 18, 17, 31, 28, 47, 51, 75, 81, 119, 134, 181, 206, 277, 323, 420, 488, 623, 737, 922, 1084, 1352, 1597, 1960, 2313, 2819, 3330, 4029, 4743, 5704, 6722, 8030, 9434, 11234, 13175, 15601, 18262, 21552, 25184, 29612, 34518

Offset: 1

Clark Kimberling, Apr 24 2019

This sequence and A325347 partition the partition numbers, A000041.

The median of a multiset is either the middle part (for odd length), or the average of the two middle parts (for even length). - Gus Wiseman, Mar 16 2023

			a(7) counts these 4 partitions: [6,1], [5,2], [4,3], [3,2,1,1].

Fausto A. C. Cariboni, Table of n, a(n) for n = 1..180

The complement is counted by A325347, strict A359907.
For mean instead of median we have A349156, strict A361391.
These partitions have ranks A359912, complement A359908.
The strict case is A360952.
A000041 counts integer partitions, strict A000009.
A008284/A058398/A327482 count partitions by mean.
A359893/A359901/A359902 count partitions by median.
Cf. A000016, A051293, A067538, A082550, A240219, A240850, A316413, A326567/A326568, A327475, A359897, A360005.

Table[Count[IntegerPartitions[n], q_ /; !IntegerQ[Median[q]]], {n, 10}]

A359907 Number of strict integer partitions of n with integer median.

Original entry on oeis.org

0, 1, 1, 1, 2, 1, 4, 2, 6, 4, 9, 6, 14, 10, 18, 16, 27, 23, 36, 34, 51, 49, 67, 68, 94, 95, 122, 129, 166, 174, 217, 233, 287, 308, 371, 405, 487, 528, 622, 683, 805, 880, 1024, 1127, 1305, 1435, 1648, 1818, 2086, 2295, 2611, 2882, 3273, 3606, 4076, 4496, 5069

Offset: 0

Gus Wiseman, Jan 21 2023

nonn

The median of a multiset is either the middle part (for odd length), or the average of the two middle parts (for even length).

			The a(1) = 1 through a(14) = 18 partitions (A..E = 10..14):
  1  2  3  4   5  6    7    8    9    A    B    C     D     E
           31     42   421  53   432  64   542  75    643   86
                  51        62   531  73   632  84    652   95
                  321       71   621  82   641  93    742   A4
                            431       91   731  A2    751   B3
                            521       532  821  B1    832   C2
                                      541       543   841   D1
                                      631       642   931   653
                                      721       651   A21   743
                                                732   6421  752
                                                741         761
                                                831         842
                                                921         851
                                                5421        932
                                                            941
                                                            A31
                                                            B21
                                                            7421

For mean instead of median: A102627, non-strict A067538 (ranked by A316413).
This is the strict case of A325347, ranked by A359908.
The median statistic is ranked by A360005(n)/2.
A000041 counts partitions, strict A000009.
A051293 counts subsets with integer mean, median A000975, cf. A005578.
A058398 counts partitions by mean, see also A008284, A327482.
A326567/A326568 gives the mean of prime indices.
A359893, A359901, A359902 count partitions by median.
Cf. A000016, A082550, A240219, A240850, A326669, A327475, A328966, A359897.

Table[Length[Select[IntegerPartitions[n],UnsameQ@@#&&IntegerQ[Median[#]]&]],{n,0,30}]

A000013 Definition (1): Number of n-bead binary necklaces with beads of 2 colors where the colors may be swapped but turning over is not allowed.

Original entry on oeis.org

1, 1, 2, 2, 4, 4, 8, 10, 20, 30, 56, 94, 180, 316, 596, 1096, 2068, 3856, 7316, 13798, 26272, 49940, 95420, 182362, 349716, 671092, 1290872, 2485534, 4794088, 9256396, 17896832, 34636834, 67110932, 130150588, 252648992, 490853416, 954444608, 1857283156, 3616828364

Offset: 0

N. J. A. Sloane

Definition (2): Equivalently, number of different output sequences from an n-stage pure cycling shift register when 2 sequences are considered the same if one is the complement of the other.
Definition (3): Also number of different output sequences from an n-stage pure cycling shift register constrained so contents have even weight.
Definition (4): Also number of output sequences from (n-1)-stage shift register which feeds back the mod 2 sum of the contents of the register.
The equivalence of definitions (1) and (2) follows at once from the definitions.
If u is an output sequence of type (2) then its derivative is of type (3) - so (2) and (3) count the same things.
If we have a shift register of type (4), append a new cell which contains the mod 2 sum of the contents to get a shift register of type (3). So (3) and (4) count the same things.
If n is even, a(n) = A000116(n/2). If 2^(n+1)-1 is prime, then a(n) = A128976(n+1), the number of cycles in the digraph of the Lucas-Lehmer operator LL(x) = x^2 - 2 acting on Z/(2^(n+1)-1). - M. F. Hasler, May 19 2007
Also number of 2n-bead balanced binary necklaces that are equivalent to their complements. - Andrew Howroyd, Sep 29 2017

			G.f. = 1 + x + 2*x^2 + 2*x^3 + 4*x^4 + 4*x^5 + 8*x^6 + 10*x^7 + 20*x^8 + ...

S. W. Golomb, Shift-Register Sequences, Holden-Day, San Francisco, 1967, p. 172.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Seiichi Manyama, Table of n, a(n) for n = 0..3334 (first 201 terms from T. D. Noe)
Nicolás Álvarez, Victória Becher, Martín Mereb, Ivo Pajor, and Carlos Miguel Soto, On extremal factors of de Bruijn-like graphs, Univ. Buenos Aires (Argentina 2023). See also arXiv:2308.16257 [math.CO], 2023. See references.
Joerg Arndt, Matters Computational (The Fxtbook), p. 151, p. 408.
Raghav Bhutani and Frederick Saia, Replacement dynamics of binary quadratic forms, arXiv:2508.05816 [math.NT], 2025. See p. 6.
Henry Bottomley, Initial terms of A000011 and A000013
Zachary E. Chin and Isaac L. Chuang, The quantum trajectory sensing problem and its solution, arXiv:2410.00893 [quant-ph], 2024. See p. 19.
N. J. Fine, Classes of periodic sequences, Illinois J. Math., 2 (1958), 285-302.
E. N. Gilbert and J. Riordan, Symmetry types of periodic sequences, Illinois J. Math., 5 (1961), 657-665.
Darij Grinberg and Peter Mao, Necklaces over a group with identity product, arXiv:2405.08937 [math.CO], 2024. See pp. 15, 22.
Karyn McLellan, Periodic coefficients and random Fibonacci sequences, Electronic Journal of Combinatorics, 20(4), 2013, #P32.
Frank Ruskey, Necklaces, Lyndon words, De Bruijn sequences, etc.
Frank Ruskey, Necklaces, Lyndon words, De Bruijn sequences, etc. [Cached copy, with permission, pdf format only]
N. J. A. Sloane, On single-deletion-correcting codes
N. J. A. Sloane, On single-deletion-correcting codes, arXiv:math/0207197 [math.CO], 2002; in Codes and Designs (Columbus, OH, 2000), 273-291, Ohio State Univ. Math. Res. Inst. Publ., 10, de Gruyter, Berlin, 2002.
N. J. A. Sloane, Maple code for this and related sequences
Index entries for sequences related to necklaces

Cf. A000031, A000016, A000116.
Cf. A128976.
Cf. A000010, A027750.
Cf. A385665, A000048.

a000013 0 = 1
a000013 n = sum (zipWith (*)
   (map (a000010 . (* 2)) ds) (map (2 ^) $ reverse ds)) `div` (2 * n)
   where ds = a027750_row n
-- Reinhard Zumkeller, Jul 08 2013

with(numtheory): A000013 := proc(n) local s,d; if n = 0 then RETURN(1) else s := 0; for d in divisors(n) do s := s+(phi(2*d)*2^(n/d))/(2*n); od; RETURN(s); fi; end;

a[n_] := Fold[ #1 + EulerPhi[2#2]2^(n/#2)/(2n) &, 0, Divisors[n]]
a[ n_] := If[ n < 1, Boole[n == 0], DivisorSum[ n, EulerPhi[2 #] 2^(n/#) &] / (2 n)]; (* Michael Somos, Dec 19 2014 *)
mx=40;CoefficientList[Series[1-Sum[EulerPhi[2i] Log[1-2*x^i]/(2i),{i,1,mx}],{x,0,mx}],x] (* Herbert Kociemba, Nov 01 2016 *)

{a(n) = if( n<1, n==0, sumdiv(n, k, eulerphi(2*k) * 2^(n/k)) / (2*n))}; /* Michael Somos, Oct 20 1999 */

from sympy import divisors, totient
def a(n): return 1 if n<1 else sum([totient(2*d)*2**(n//d) for d in divisors(n)])//(2*n) # Indranil Ghosh, Apr 28 2017

a(n) = Sum_{ d divides n } (phi(2*d)*2^(n/d))/(2*n) for n>0. - Michael Somos, Oct 20 1999
G.f.: 1 - Sum_{i>=1} phi(2*i)*log(1-2*x^i)/(2*i). - Herbert Kociemba, Nov 01 2016
From Richard L. Ollerton, May 11 2021: (Start)
For n >= 1:
a(n) = (1/(2*n))*Sum_{k=1..n} phi(2*gcd(n,k))*2^(n/gcd(n,k))/phi(n/gcd(n,k)), where phi = A000010.
a(n) = (1/(2*n))*Sum_{k=1..n} phi(2*n/gcd(n,k))*2^gcd(n,k)/phi(n/gcd(n,k)). (End)
a(n) ~ 2^(n-1)/n. - Cedric Lorand, Apr 24 2022
a(n) = Sum_{k=1..n} A385665(n,k) = Sum_{d|n} A000048(d). - Tilman Piesk, Jul 31 2025

A327475 Number of subsets of {1..n} whose mean is an integer, where {} has mean 0.

Original entry on oeis.org

1, 2, 3, 6, 9, 16, 27, 46, 77, 136, 239, 426, 769, 1400, 2571, 4762, 8857, 16568, 31139, 58734, 111165, 211044, 401695, 766418, 1465489, 2807672, 5388783, 10359850, 19946833, 38459624, 74251095, 143524762, 277742489, 538043664, 1043333935, 2025040766, 3933915349

Offset: 0

Gus Wiseman, Sep 13 2019

nonn

			The a(0) = 1 through a(5) = 16 subsets:
  {}  {}   {}   {}       {}       {}
      {1}  {1}  {1}      {1}      {1}
           {2}  {2}      {2}      {2}
                {3}      {3}      {3}
                {1,3}    {4}      {4}
                {1,2,3}  {1,3}    {5}
                         {2,4}    {1,3}
                         {1,2,3}  {1,5}
                         {2,3,4}  {2,4}
                                  {3,5}
                                  {1,2,3}
                                  {1,3,5}
                                  {2,3,4}
                                  {3,4,5}
                                  {1,2,4,5}
                                  {1,2,3,4,5}

If the subset is required to contain n, we get A063776.

Cf. A000016, A051293, A065795, A082550, A135342, A327474, A327481.

with(numtheory):
b:= n-> add(2^(n/d)*phi(d), d=select(x-> x::odd, divisors(n)))/n:
a:= proc(n) option remember; `if`(n=0, 1, b(n)-1+a(n-1)) end:
seq(a(n), n=0..36);  # Alois P. Heinz, Jan 13 2024

Table[Length[Select[Subsets[Range[n]],#=={}||IntegerQ[Mean[#]]&]],{n,0,10}]

from sympy import totient, divisors
def A327475(n): return sum((sum(totient(d)<>(~k&k-1).bit_length(),generator=True))<<1)//k for k in range(1,n+1))-n+1 # Chai Wah Wu, Feb 22 2023

a(n) = A051293(n) + 1.

A327481 Triangle read by rows where T(n,k) is the number of nonempty subsets of {1..n} with mean k.

Original entry on oeis.org

1, 1, 1, 1, 3, 1, 1, 3, 3, 1, 1, 3, 7, 3, 1, 1, 3, 9, 9, 3, 1, 1, 3, 9, 19, 9, 3, 1, 1, 3, 9, 25, 25, 9, 3, 1, 1, 3, 9, 29, 51, 29, 9, 3, 1, 1, 3, 9, 31, 75, 75, 31, 9, 3, 1, 1, 3, 9, 31, 93, 151, 93, 31, 9, 3, 1, 1, 3, 9, 31, 105, 235, 235, 105, 31, 9, 3, 1

Offset: 1

Gus Wiseman, Sep 13 2019

All terms are odd.

			Triangle begins:
                         1
                       1   1
                     1   3   1
                   1   3   3   1
                 1   3   7   3   1
               1   3   9   9   3   1
             1   3   9  19   9   3   1
           1   3   9  25  25   9   3   1
         1   3   9  29  51  29   9   3   1
       1   3   9  31  75  75  31   9   3   1
     1   3   9  31  93 151  93  31   9   3   1
   1   3   9  31 105 235 235 105  31   9   3   1
The subsets counted in row n = 5:
  {1}  {2}      {3}          {4}      {5}
       {1,3}    {1,5}        {3,5}
       {1,2,3}  {2,4}        {3,4,5}
                {1,3,5}
                {2,3,4}
                {1,2,4,5}
                {1,2,3,4,5}

Row sums are A051293.
The sequence of rows converges to A066571.
The version for partitions is A327482.
Cf. A000016, A063776, A065795, A135342, A327474, A327475, A327483, A327484.

Table[Length[Select[Subsets[Range[n]],Mean[#]==k&]],{n,10},{k,n}]

A068009 Square array T(m,n) with m (row) >= 1 and n (column) >= 0 read by antidiagonals: number of subsets of {1,2,3,...n} that sum to 0 mod m (including the empty set, whose sum is 0).

Original entry on oeis.org

1, 2, 1, 4, 1, 1, 8, 2, 1, 1, 16, 4, 2, 1, 1, 32, 8, 4, 1, 1, 1, 64, 16, 6, 2, 1, 1, 1, 128, 32, 12, 4, 2, 1, 1, 1, 256, 64, 24, 8, 4, 2, 1, 1, 1, 512, 128, 44, 16, 8, 3, 1, 1, 1, 1, 1024, 256, 88, 32, 14, 6, 3, 1, 1, 1, 1, 2048, 512, 176, 64, 26, 12, 5, 2, 1, 1, 1, 1, 4096, 1024, 344, 128, 52, 22, 10, 4, 2, 1, 1, 1, 1

Offset: 0

Antti Karttunen, Feb 11 2002

When p is an odd prime, T(p,k+p) = 2*T(p,k) + (2^k * ((2^p) - 2)/p) for all k >= 0. [Sophie LeBlanc]
When m divides n (with n >= m), T(m,n) = (1/m) Sum_{d | m and d is odd} phi(d) * 2^(n/d). [N. Kitchloo and L. Pachter; D. Rusin]
A068009(C(i+1,2), i) = 2, A068009(C(i,2)+1, i) = A000009(i-1) + 1. [AK, cf. A068049]

			Table for T(m,n) (with rows m >= 1 and columns n >= 0) begins as follows:
  1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, ...
  1, 1, 2, 4,  8, 16, 32,  64, 128, 256,  512, 1024, ...
  1, 1, 2, 4,  6, 12, 24,  44,  88, 176,  344, ...
  1, 1, 1, 2,  4,  8, 16,  32,  64, 128,  ...
  1, 1, 1, 2,  4,  8, 14,  26,  52, ...
  1, 1, 1, 2,  3,  6, 12,  22, ...
  1, 1, 1, 1,  3,  5, 10, ...
  1, 1, 1, 1,  2,  4, ...
  1, 1, 1, 1,  2, ...
  1, 1, 1, 1, ...
  1, 1, 1, ...
  1, 1, ...
  1, ...
  ...

Alois P. Heinz, Antidiagonals n = 0..140, flattened
Antti Karttunen, Scheme code for computing this table and its rows.
N. Kitchloo and L. Pachter, An interesting result about subset sums, Nov 27 1993.
William Kuszmaul, A new approach to enumerating statistics modulo n, arXiv:1402.3839 [math.CO], 2014.
Lior Pachter, Subset sums, 2015.
Bill Pet, Sophie LeBlanc, Will Self et al., Subsets of {1,2,3,...,n} (discussion in sci.math).
R. P. Stanley and M. F. Yoder, A study of Varshamov codes for asymmetric channels, JPL Technical Report 32-1526, Vol. XIV (1972), 117-123.
Index entries for sequences related to subset sums mod m

Main diagonal: A000016, superdiagonal: A063776. The first term greater than one occurs on each row m in the position A002024(m) and these are given in A068049.

Row 1: A000079, row 2: A011782, row 3: A068010, row 5: A068011, row 6: A068012, row 7: A068013, row 9: A068030, row 10: A068031, row 11: A068032, row 12: A068033, row 13: A068034, row 14: A068035, row 15: A068036, row 16: A068037, row 17: A068038, row 18: A068039, row 19: A068040, row 20: A068041, row 21: A068042, row 25: A068043, row 32: A068044, row 64: A068045.

b:= proc(n, m, t) option remember; `if`(n=0, `if`(t=0, 1, 0),
       b(n-1, m, t)+ b(n-1, m, irem(t+n,m)))
    end:
T:= (m, n)-> b(n, m, 0):
seq(seq(T(1+m, d-m), m=0..d), d=0..12);  # Alois P. Heinz, Jan 18 2014

max = 13; row[m_] := (ClearAll[t]; im = IdentityMatrix[m]; v = Join[ {Last[im]}, Most[im] ]; t[0] = im[[1]]; t[k_] := t[k] = (im + MatrixPower[v, k]) . t[k-1]; Table[ t[k][[1]], {k, 0, max}]); rows = Table[ row[m], {m, 1, max}]; A068009 = Flatten[ Table[ rows[[m-n+1, n]], {m, 1, max, 1}, {n, m, 1, -1}]] (* Jean-François Alcover, Apr 02 2012, after Will Self *)
b[n_, m_, t_] := b[n, m, t] = If[n == 0, If[t == 0, 1, 0], b[n-1, m, t]+b[n-1, m, Mod[t+n, m]]]; T[m_, n_] := b[n, m, 0]; Table[Table[T[1+m, d-m], {m, 0, d}], {d, 0, 12}] // Flatten (* Jean-François Alcover, Jan 13 2015, after Alois P. Heinz *)

A063776 Number of subsets of {1,2,...,n} which sum to 0 modulo n.

Original entry on oeis.org

2, 2, 4, 4, 8, 12, 20, 32, 60, 104, 188, 344, 632, 1172, 2192, 4096, 7712, 14572, 27596, 52432, 99880, 190652, 364724, 699072, 1342184, 2581112, 4971068, 9586984, 18512792, 35791472, 69273668, 134217728, 260301176, 505290272, 981706832

Offset: 1

Ahmed Fares (ahmedfares(AT)my-deja.com), Aug 16 2001

From Gus Wiseman, Sep 14 2019: (Start)
Also the number of subsets of {1..n} that are empty or contain n and have integer mean. If the subsets are not required to contain n, we get A327475. For example, the a(1) = 2 through a(6) = 12 subsets are:
  {}   {}   {}       {}       {}           {}
  {1}  {2}  {3}      {4}      {5}          {6}
            {1,3}    {2,4}    {1,5}        {2,6}
            {1,2,3}  {2,3,4}  {3,5}        {4,6}
                              {1,3,5}      {1,2,6}
                              {3,4,5}      {1,5,6}
                              {1,2,4,5}    {2,4,6}
                              {1,2,3,4,5}  {4,5,6}
                                           {1,2,3,6}
                                           {1,4,5,6}
                                           {2,3,5,6}
                                           {2,3,4,5,6}
(End)

			G.f. = 2*x + 2*x^2 + 4*x^3 + 4*x^4 + 8*x^5 + 12*x^6 + 20*x^7 + 32*x^8 + 60*x^9 + ...

Seiichi Manyama, Table of n, a(n) for n = 1..3333 (first 200 terms from T. D. Noe)
T. Amdeberhan, M. Can and V. Moll, Broken bracelets, Molien series, paraffin wax and the elliptic curve 48a4, SIAM Journal of Discrete Math., v.25, 2011, p. 1843. See equation (1.2).
Juhani Karhumäki, S. Puzynina, M. Rao, and M. A. Whiteland, On cardinalities of k-abelian equivalence classes, arXiv preprint arXiv:1605.03319 [math.CO], 2016.
N. Kitchloo and L. Pachter, An interesting result about subset sums, preprint (pdf file), 1993.
N. Kitchloo and L. Pachter, An interesting result about subset sums, preprint (pdf file), 1993.

The superdiagonal of A068009.
Cf. A000010, A000013, A051293, A053633, A053634, A053636, A054539, A082550.
Cf. A000016, A065795, A327475, A327481.

a063776 n = a053636 n `div` n  -- Reinhard Zumkeller, Sep 13 2013

Table[a = Select[ Divisors[n], OddQ[ # ] &]; Apply[Plus, 2^(n/a)*EulerPhi[a]]/n, {n, 1, 35}]
a[ n_] := If[ n < 1, 0, 1/n Sum[ Mod[ d, 2] EulerPhi[ d] 2^(n / d), {d, Divisors[ n]}]]; (* Michael Somos, May 09 2013 *)
Table[Length[Select[Subsets[Range[n]],#=={}||MemberQ[#,n]&&IntegerQ[Mean[#]]&]],{n,0,10}] (* Gus Wiseman, Sep 14 2019 *)

{a(n) = if( n<1, 0, 1 / n * sumdiv( n, d, (d % 2) * eulerphi(d) * 2^(n / d)))}; /* Michael Somos, May 09 2013 */

a(n) = sumdiv(n, d, (d%2)* 2^(n/d)*eulerphi(d))/n; \\ Michel Marcus, Feb 10 2016

from sympy import totient, divisors
def A063776(n): return (sum(totient(d)<>(~n&n-1).bit_length(),generator=True))<<1)//n # Chai Wah Wu, Feb 21 2023

a(n) = (1/n) * Sum_{d divides n and d is odd} 2^(n/d) * phi(d).
a(n) = (1/n) * A053636(n). - Michael Somos, May 09 2013
a(n) = 2 * A000016(n).
For odd n, a(n) = A000031(n).
G.f.: -Sum_{m >= 0} (phi(2*m + 1)/(2*m + 1)) * log(1 - 2*x^(2*m + 1)). - Petros Hadjicostas, Jul 13 2019
a(n) = A082550(n) + 1. - Gus Wiseman, Sep 14 2019

More terms from Vladeta Jovovic, Aug 20 2001

A065795 Number of subsets of {1,2,...,n} that contain the average of their elements.

Original entry on oeis.org

1, 2, 4, 6, 10, 16, 26, 42, 72, 124, 218, 390, 706, 1292, 2388, 4436, 8292, 15578, 29376, 55592, 105532, 200858, 383220, 732756, 1403848, 2694404, 5179938, 9973430, 19229826, 37125562, 71762396, 138871260, 269021848, 521666984, 1012520400, 1966957692, 3824240848

Offset: 1

John W. Layman, Dec 05 2001

nonn

Also the number of subsets of {1,2,...,n} with sum of entries divisible by the largest element (compare A000016). See the Palmer Melbane link for a bijection. - Joel B. Lewis, Nov 13 2014

			a(4)=6, since {1}, {2}, {3}, {4}, {1,2,3} and {2,3,4} contain their averages.
From _Gus Wiseman_, Sep 14 2019: (Start)
The a(1) = 1 through a(6) = 16 subsets:
  {1}  {1}  {1}      {1}      {1}          {1}
       {2}  {2}      {2}      {2}          {2}
            {3}      {3}      {3}          {3}
            {1,2,3}  {4}      {4}          {4}
                     {1,2,3}  {5}          {5}
                     {2,3,4}  {1,2,3}      {6}
                              {1,3,5}      {1,2,3}
                              {2,3,4}      {1,3,5}
                              {3,4,5}      {2,3,4}
                              {1,2,3,4,5}  {2,4,6}
                                           {3,4,5}
                                           {4,5,6}
                                           {1,2,3,6}
                                           {1,4,5,6}
                                           {1,2,3,4,5}
                                           {2,3,4,5,6}
(End)

Alois P. Heinz, Table of n, a(n) for n = 1..3333
Palmer Melbane, Combinations under constraint, Art of Problem Solving thread. - _Joel B. Lewis_, Nov 13 2014

Subsets containing n whose mean is an element are A000016.
The version for integer partitions is A237984.
Subsets not containing their mean are A327471.
Cf. A051293, A063776, A066571, A135342, A324736, A325705, A326083, A326836, A327478, A327481.

Table[ Sum[a = Select[Divisors[i], OddQ[ # ] &]; Apply[ Plus, 2^(i/a) * EulerPhi[a]]/i, {i, n}]/2, {n, 34}]
(* second program *)
Table[Length[Select[Subsets[Range[n]],MemberQ[#,Mean[#]]&]],{n,0,10}] (* Gus Wiseman, Sep 14 2019 *)

a(n) = (1/2)*sum(i=1, n, (1/i)*sumdiv(i, d, if (d%2, 2^(i/d)*eulerphi(d)))); \\ Michel Marcus, Dec 20 2020

from sympy import totient, divisors
def A065795(n): return sum((sum(totient(d)<>(~k&k-1).bit_length(),generator=True))<<1)//k for k in range(1,n+1))>>1 # Chai Wah Wu, Feb 22 2023

a(n) = (1/2)*Sum_{i=1..n} (f(i) - 1) where f(i) = (1/i) * Sum_{d | i and d is odd} 2^(i/d) * phi(d).
a(n) = (n + A051293(n))/2.
a(n) = 2^n - A327471(n). - Gus Wiseman, Sep 14 2019

Edited and extended by Robert G. Wilson v, Nov 15 2002

A359899 Number of strict odd-length integer partitions of n whose parts have the same mean as median.

Original entry on oeis.org

0, 1, 1, 1, 1, 1, 2, 1, 1, 3, 1, 1, 4, 1, 1, 6, 1, 1, 6, 1, 5, 7, 1, 1, 8, 12, 1, 9, 2, 1, 33, 1, 1, 11, 1, 50, 12, 1, 1, 13, 70, 1, 46, 1, 1, 122, 1, 1, 16, 102, 155, 17, 1, 1, 30, 216, 258, 19, 1, 1, 310, 1, 1, 666, 1, 382, 23, 1, 1, 23, 1596, 1, 393, 1, 1

Offset: 0

Gus Wiseman, Jan 20 2023

nonn

			The a(30) = 33 partitions:
  (30)  (11,10,9)  (8,7,6,5,4)
        (12,10,8)  (9,7,6,5,3)
        (13,10,7)  (9,8,6,4,3)
        (14,10,6)  (9,8,6,5,2)
        (15,10,5)  (10,7,6,4,3)
        (16,10,4)  (10,7,6,5,2)
        (17,10,3)  (10,8,6,4,2)
        (18,10,2)  (10,8,6,5,1)
        (19,10,1)  (10,9,6,3,2)
                   (10,9,6,4,1)
                   (11,7,6,4,2)
                   (11,7,6,5,1)
                   (11,8,6,3,2)
                   (11,8,6,4,1)
                   (11,9,6,3,1)
                   (12,7,6,3,2)
                   (12,7,6,4,1)
                   (12,8,6,3,1)
                   (12,9,6,2,1)
                   (13,7,6,3,1)
                   (13,8,6,2,1)
                   (14,7,6,2,1)
                   (11,10,6,2,1)

Andrew Howroyd, Table of n, a(n) for n = 0..1000

Strict odd-length case of A240219, complement A359894, ranked by A359889.
Strict case of A359895, complement A359896, ranked by A359891.
Odd-length case of A359897, complement A359898.
The complement is counted by A359900.
A000041 counts partitions, strict A000009.
A008284/A058398/A327482 count partitions by mean, ranked by A326567/A326568.
A008289 counts strict partitions by mean.
A027193 counts odd-length partitions, strict A067659, ranked by A026424.
A067538 counts ptns with integer mean, strict A102627, ranked by A316413.
A237984 counts ptns containing their mean, strict A240850, ranked by A327473.
A325347 counts ptns with integer median, strict A359907, ranked by A359908.
A359893 and A359901 count partitions by median, odd-length A359902.
Cf. A000016, A065795, A066571, A240851, A359903, A359906, A359910.

Table[Length[Select[IntegerPartitions[n], UnsameQ@@#&&OddQ[Length[#]]&&Mean[#]==Median[#]&]],{n,0,30}]

\\ Q(n,k,m) is g.f. for k strict parts of max size m.
Q(n,k,m)={polcoef(prod(i=1, m, 1 + y*x^i + O(x*x^n)), k, y)}
a(n)={if(n==0, 0, sumdiv(n, d, if(d%2, my(m=n/d, h=d\2, r=n-m*(h+1)); if(r>=h*(h+1), polcoef(Q(r, h, m-1)*Q(r, h, r), r)))))} \\ Andrew Howroyd, Jan 21 2023

a(p) = 1 for prime p. - Andrew Howroyd, Jan 21 2023

A359906 Number of integer partitions of n with integer mean and integer median.

Original entry on oeis.org

1, 2, 2, 4, 2, 8, 2, 10, 9, 14, 2, 39, 2, 24, 51, 49, 2, 109, 2, 170, 144, 69, 2, 455, 194, 116, 381, 668, 2, 1378, 2, 985, 956, 316, 2043, 4328, 2, 511, 2293, 6656, 2, 8634, 2, 8062, 14671, 1280, 2, 26228, 8035, 15991, 11614, 25055, 2, 47201, 39810, 65092

Offset: 1

Gus Wiseman, Jan 21 2023

nonn

The median of a multiset is either the middle part (for odd length), or the average of the two middle parts (for even length).

			The a(1) = 1 through a(9) = 9 partitions:
  1  2   3    4     5      6       7        8         9
     11  111  22    11111  33      1111111  44        333
              31           42               53        432
              1111         51               62        441
                           222              71        522
                           321              2222      531
                           411              3221      621
                           111111           3311      711
                                            5111      111111111
                                            11111111

For just integer mean we have A067538, strict A102627, ranked by A316413.
For just integer median we have A325347, strict A359907, ranked by A359908.
These partitions are ranked by A360009.
A000041 counts partitions, strict A000009.
A058398 counts partitions by mean, see also A008284, A327482.
A051293 counts subsets with integer mean, median A000975.
A326567/A326568 gives mean of prime indices.
A326622 counts factorizations with integer mean, strict A328966.
A359893/A359901/A359902 count partitions by median.
A360005(n)/2 gives median of prime indices.
Cf. A000016, A082550, A237984, A240219, A326669, A327475, A349156, A359894, A359897, A359905.

Table[Length[Select[IntegerPartitions[n], IntegerQ[Mean[#]]&&IntegerQ[Median[#]]&]],{n,1,30}]

cp's OEIS Frontend

A307683 Number of partitions of n having a non-integer median.

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A359907 Number of strict integer partitions of n with integer median.

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A000013 Definition (1): Number of n-bead binary necklaces with beads of 2 colors where the colors may be swapped but turning over is not allowed.

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A327475 Number of subsets of {1..n} whose mean is an integer, where {} has mean 0.

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A327481 Triangle read by rows where T(n,k) is the number of nonempty subsets of {1..n} with mean k.

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A068009 Square array T(m,n) with m (row) >= 1 and n (column) >= 0 read by antidiagonals: number of subsets of {1,2,3,...n} that sum to 0 mod m (including the empty set, whose sum is 0).

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A063776 Number of subsets of {1,2,...,n} which sum to 0 modulo n.

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