A067539 -id:A067539 - cp's OEIS frontend

A326647 Number of factorizations of n into factors > 1 with integer average and integer geometric mean.

0, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 1, 1, 1, 1, 4, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 6, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 4, 1, 1, 1, 1, 1, 1, 1

Offset: 1

Gus Wiseman, Jul 16 2019

nonn

			The a(216) = 5 factorizations:
  (2*4*27)
  (3*3*24)
  (3*6*12)
  (6*6*6)
  (216)
The a(729) = 8 factorizations:
  (3*3*3*3*3*3)
  (3*3*81)
  (3*9*27)
  (3*243)
  (9*9*9)
  (9*81)
  (27*27)
  (729)

Wikipedia, Geometric mean

Positions of terms > 1 are the perfect powers A001597.
Factorizations with integer average are A326622.
Factorizations with integer geometric mean are A326028.
Partitions with integer average and geometric mean are A326641.
Cf. A001055, A067538, A067539, A322794, A326514, A326515, A326516, A326623, A326643, A326645.

facs[n_]:=If[n<=1,{{}},Join@@Table[Map[Prepend[#,d]&,Select[facs[n/d],Min@@#>=d&]],{d,Rest[Divisors[n]]}]];
Table[Length[Select[facs[n],IntegerQ[Mean[#]]&&IntegerQ[GeometricMean[#]]&]],{n,2,100}]

A326673 The positions of ones in the reversed binary expansion of n have integer geometric mean.

Original entry on oeis.org

1, 2, 4, 8, 9, 11, 16, 32, 64, 128, 130, 138, 256, 257, 261, 264, 296, 388, 420, 512, 1024, 2048, 2052, 2084, 2306, 2316, 2338, 2348, 4096, 8192, 16384, 32768, 32769, 32776, 32777, 32899, 32904, 32907, 33024, 35072, 65536, 131072, 131074, 131084, 131106

Offset: 1

Gus Wiseman, Jul 17 2019

			The reversed binary expansion of 11 is (1,1,0,1) and {1,2,4} has integer geometric mean, so 11 is in the sequence.

Andrew Howroyd, Table of n, a(n) for n = 1..211
Wikipedia, Geometric mean

Partitions with integer geometric mean are A067539.
Subsets with integer geometric mean are A326027.
Factorizations with integer geometric mean are A326028.
Numbers whose binary digit positions have integer mean are A326669.
Numbers whose binary digit positions are relatively prime are A326674.
Numbers whose binary digit positions have integer geometric mean are A326672.
Cf. A000120, A051293, A070939, A291166, A326625.

Select[Range[1000],IntegerQ[GeometricMean[Join@@Position[Reverse[IntegerDigits[#,2]],1]]]&]

ok(n)={ispower(prod(i=0, logint(n,2), if(bittest(n,i), i+1, 1)), hammingweight(n))}
{ for(n=1, 10^7, if(ok(n), print1(n, ", "))) } \\ Andrew Howroyd, Sep 29 2019

A326643 Number of subsets of {1..n} whose mean and geometric mean are both integers.

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 6, 7, 9, 11, 12, 13, 16, 17, 18, 19, 22, 23, 30, 31, 32, 33, 34, 35, 41, 46, 47, 70, 71, 72, 73, 74, 102, 103, 104, 105, 143, 144, 145, 146, 151, 152, 153, 154, 155, 161, 162, 163, 244, 252, 280, 281, 282, 283, 409, 410, 416, 417, 418, 419

Offset: 0

Gus Wiseman, Jul 16 2019

nonn

			The a(1) = 1 through a(12) = 16 subsets:
  {1}  {1}  {1}  {1}  {1}  {1}  {1}  {1}    {1}    {1}    {1}    {1}
       {2}  {2}  {2}  {2}  {2}  {2}  {2}    {2}    {2}    {2}    {2}
            {3}  {3}  {3}  {3}  {3}  {3}    {3}    {3}    {3}    {3}
                 {4}  {4}  {4}  {4}  {4}    {4}    {4}    {4}    {4}
                      {5}  {5}  {5}  {5}    {5}    {5}    {5}    {5}
                           {6}  {6}  {6}    {6}    {6}    {6}    {6}
                                {7}  {7}    {7}    {7}    {7}    {7}
                                     {8}    {8}    {8}    {8}    {8}
                                     {2,8}  {9}    {9}    {9}    {9}
                                            {1,9}  {10}   {10}   {10}
                                            {2,8}  {1,9}  {11}   {11}
                                                   {2,8}  {1,9}  {12}
                                                          {2,8}  {1,9}
                                                                 {2,8}
                                                                 {3,6,12}
                                                                 {3,4,9,12}

David Wasserman, Table of n, a(n) for n = 0..119
Wikipedia, Geometric mean

Partial sums of A326644.
Subsets whose geometric mean is an integer are A326027.
Subsets whose mean is an integer are A051293.
Partitions with integer mean and geometric mean are A326641.
Strict partitions with integer mean and geometric mean are A326029.
Cf. A067538, A067539, A078175, A082553, A102627, A326623, A326625, A326645, A326646, A326647.

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

More terms from David Wasserman, Aug 03 2019

A326624 Heinz numbers of non-constant integer partitions whose geometric mean is an integer.

Original entry on oeis.org

14, 42, 46, 57, 76, 106, 126, 161, 183, 185, 194, 196, 228, 230, 302, 371, 378, 393, 399, 412, 424, 454, 477, 515, 588, 622, 679, 684, 687, 722, 742, 781, 786, 838, 1057, 1064, 1077, 1082, 1115, 1134, 1150, 1157, 1159, 1219, 1244, 1272, 1322, 1563, 1589, 1654

Offset: 1

Gus Wiseman, Jul 14 2019

nonn

The Heinz number of an integer partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k).

			The sequence of terms together with their prime indices begins:
    14: {1,4}
    42: {1,2,4}
    46: {1,9}
    57: {2,8}
    76: {1,1,8}
   106: {1,16}
   126: {1,2,2,4}
   161: {4,9}
   183: {2,18}
   185: {3,12}
   194: {1,25}
   196: {1,1,4,4}
   228: {1,1,2,8}
   230: {1,3,9}
   302: {1,36}
   371: {4,16}
   378: {1,2,2,2,4}
   393: {2,32}
   399: {2,4,8}
   412: {1,1,27}

Wikipedia, Geometric mean

The case with prime powers is A326623.
Subsets whose geometric mean is an integer are A326027.
Cf. A001055, A067539, A078175, A102627, A316413, A326567/A326568, A326622, A326625.

primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[100],!PrimePowerQ[#]&&IntegerQ[GeometricMean[primeMS[#]]]&]

A340606 Numbers whose prime indices (A112798) are all divisors of the number of prime factors (A001222).

Original entry on oeis.org

1, 2, 4, 6, 8, 9, 16, 20, 24, 32, 36, 50, 54, 56, 64, 81, 84, 96, 125, 126, 128, 144, 160, 176, 189, 196, 216, 240, 256, 294, 324, 360, 384, 400, 416, 441, 486, 512, 540, 576, 600, 624, 686, 729, 810, 864, 896, 900, 936, 968, 1000, 1024, 1029, 1040, 1088, 1215

Offset: 1

Gus Wiseman, Jan 24 2021

nonn

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

			The sequence of terms together with their prime indices begins:
   1: {}
   2: {1}
   4: {1,1}
   6: {1,2}
   8: {1,1,1}
   9: {2,2}
  16: {1,1,1,1}
  20: {1,1,3}
  24: {1,1,1,2}
  32: {1,1,1,1,1}
  36: {1,1,2,2}
  50: {1,3,3}
  54: {1,2,2,2}
  56: {1,1,1,4}
  64: {1,1,1,1,1,1}
  81: {2,2,2,2}
  84: {1,1,2,4}
  96: {1,1,1,1,1,2}

Note: Heinz numbers are given in parentheses below.
The reciprocal version is A143773 (A316428).
These partitions are counted by A340693.
A120383 lists numbers divisible by all of their prime indices.
A324850 lists numbers divisible by the product of their prime indices.
A003963 multiplies together the prime indices of n.
A018818 counts partitions of n into divisors of n (A326841).
A047993 counts balanced partitions (A106529).
A067538 counts partitions of n whose length divides n (A316413).
A056239 adds up the prime indices of n.
A061395 selects the maximum prime index.
A067538 counts partitions of n whose maximum divides n (A326836).
A072233 counts partitions by sum and length.
A112798 lists the prime indices of each positive integer.
A168659 = partitions whose length is divisible by their maximum (A340609).
A168659 = partitions whose maximum is divisible by their length (A340610).
A289509 lists numbers with relatively prime prime indices.
A326842 = partitions of n whose length and parts all divide n (A326847).
A326843 = partitions of n whose length and maximum both divide n (A326837).
A340852 have a factorization with factors dividing length.
Cf. A000720, A001222, A006141, A067539, A200750, A298423, A324925, A326149/A326155, A340608, A340827.

primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
Select[Range[100],And@@IntegerQ/@(PrimeOmega[#]/primeMS[#])&]

A362559 Number of integer partitions of n whose weighted sum is divisible by n.

Original entry on oeis.org

1, 1, 2, 1, 2, 3, 3, 3, 5, 4, 5, 7, 8, 11, 14, 14, 18, 25, 28, 26, 42, 47, 52, 73, 77, 100, 118, 122, 158, 188, 219, 266, 313, 367, 412, 489, 578, 698, 809, 914, 1094, 1268, 1472, 1677, 1948, 2305, 2656, 3072, 3527, 4081, 4665, 5342, 6225, 7119, 8150, 9408

Offset: 1

Gus Wiseman, Apr 24 2023

nonn

The (one-based) weighted sum of a sequence (y_1,...,y_k) is Sum_{i=1..k} i*y_i. This is also the sum of partial sums of the reverse.
Also the number of n-multisets of positive integers that (1) have integer mean, (2) cover an initial interval, and (3) have weakly decreasing multiplicities.
Conjecture: A partition of n has weighted sum divisible by n iff its reverse has weighted sum divisible by n.

			The weighted sum of y = (4,2,2,1) is 1*4+2*2+3*2+4*1 = 18, which is a multiple of 9, so y is counted under a(9).
The a(1) = 1 through a(9) = 5 partitions:
  (1)  (2)  (3)    (4)  (5)      (6)     (7)        (8)       (9)
            (111)       (11111)  (222)   (3211)     (3311)    (333)
                                 (3111)  (1111111)  (221111)  (4221)
                                                              (222111)
                                                              (111111111)

For median instead of mean we have A362558.
The complement is counted by A362560.
A000041 counts integer partitions, strict A000009.
A008284/A058398/A327482 count partitions by mean.
A264034 counts partitions by weighted sum.
A304818 = weighted sum of prime indices, row-sums of A359361.
A318283 = weighted sum of reversed prime indices, row-sums of A358136.
Cf. A001227, A051293, A067538, A067539, A240219, A261079, A322439, A326622, A359893, A360068, A360069, A362051.

Table[Length[Select[IntegerPartitions[n], Divisible[Total[Accumulate[Reverse[#]]],n]&]],{n,30}]

A326672 The positions of ones in the binary expansion of n have integer geometric mean.

Original entry on oeis.org

1, 2, 4, 8, 9, 13, 16, 18, 26, 32, 36, 52, 64, 72, 104, 128, 144, 208, 256, 257, 288, 321, 416, 512, 514, 576, 642, 832, 1024, 1028, 1152, 1284, 1664, 2048, 2056, 2304, 2568, 3328, 4096, 4112, 4608, 5136, 6656, 8192, 8224, 9216, 10272, 13312, 16384, 16448

Offset: 1

Gus Wiseman, Jul 17 2019

Amiram Eldar, Table of n, a(n) for n = 1..500
Wikipedia, Geometric mean.

Partitions with integer geometric mean are A067539.
Subsets with integer geometric mean are A326027.
Factorizations with integer geometric mean are A326028.
Numbers whose binary expansion positions have integer mean are A326669.
Numbers whose binary expansion positions are relatively prime are A326674.
Numbers whose reversed binary expansion positions have integer geometric mean are A326673.
Cf. A000120, A051293, A070939, A291166, A326625.

Select[Range[100],IntegerQ[GeometricMean[Join@@Position[IntegerDigits[#,2],1]]]&]

A271654 a(n) = Sum_{k|n} binomial(n-1,k-1).

Original entry on oeis.org

1, 2, 2, 5, 2, 17, 2, 44, 30, 137, 2, 695, 2, 1731, 1094, 6907, 2, 30653, 2, 97244, 38952, 352739, 2, 1632933, 10628, 5200327, 1562602, 20357264, 2, 87716708, 2, 303174298, 64512738, 1166803145, 1391282, 4978661179, 2, 17672631939, 2707475853, 69150651910, 2, 286754260229, 2, 1053966829029, 115133177854, 4116715363847, 2, 16892899722499, 12271514, 63207357886437

Offset: 1

Franklin T. Adams-Watters, Apr 11 2016

nonn

Also the number of compositions of n whose length divides n, i.e., compositions with integer mean, ranked by A096199. - Gus Wiseman, Sep 28 2022

			From _Gus Wiseman_, Sep 28 2022: (Start)
The a(1) = 1 through a(6) = 17 compositions with integer mean:
  (1)  (2)    (3)      (4)        (5)          (6)
       (1,1)  (1,1,1)  (1,3)      (1,1,1,1,1)  (1,5)
                       (2,2)                   (2,4)
                       (3,1)                   (3,3)
                       (1,1,1,1)               (4,2)
                                               (5,1)
                                               (1,1,4)
                                               (1,2,3)
                                               (1,3,2)
                                               (1,4,1)
                                               (2,1,3)
                                               (2,2,2)
                                               (2,3,1)
                                               (3,1,2)
                                               (3,2,1)
                                               (4,1,1)
                                               (1,1,1,1,1,1)
(End)

Alois P. Heinz, Table of n, a(n) for n = 1..3329

Cf. A056045.
The version for nonempty subsets is A051293, geometric A326027.
The version for partitions is A067538, ranked by A316413, strict A102627.
These compositions are ranked by A096199.
The version for factorizations is A326622, geometric A326028.
A011782 counts compositions.
A067539 = partitions w integer geo mean, ranked by A326623, strict A326625.
A100346 counts compositions into divisors, partitions A018818.
Cf. A000041, A078174, A078175, A326567/A326568, A326624, A326641, A326836, A326837, A326843.

a:= n-> add(binomial(n-1, d-1), d=numtheory[divisors](n)):
seq(a(n), n=1..50);  # Alois P. Heinz, Dec 03 2023

Table[Length[Join @@ Permutations/@Select[IntegerPartitions[n],IntegerQ[Mean[#]]&]],{n,15}] (* Gus Wiseman, Sep 28 2022 *)

PARI
```
a(n)=sumdiv(n,k,binomial(n-1,k-1))
```

A082553 Number of sets of distinct positive integers whose geometric mean is an integer, the largest integer of a set is n.

Original entry on oeis.org

1, 1, 1, 3, 1, 1, 1, 3, 7, 1, 1, 7, 1, 1, 1, 9, 1, 29, 1, 3, 1, 1, 1, 31, 15, 1, 87, 3, 1, 1, 1, 115, 1, 1, 1, 257, 1, 1, 1, 17, 1, 1, 1, 3, 21, 1, 1, 519, 23, 141, 1, 3, 1, 847, 1, 19, 1, 1, 1, 215, 1, 1, 27, 1557, 1, 1, 1, 3, 1, 1, 1, 2617, 1, 1, 3125, 3, 1, 1

Offset: 1

Naohiro Nomoto, May 03 2003

nonn

a(n) = 1 if and only if n is squarefree (i.e., if and only if n is in A005117). - Nathaniel Johnston, Apr 28 2011

If n has a prime divisor p > sqrt(n), then a(n) = a(n/p). - Max Alekseyev, Aug 27 2013

			a(4) = 3: the three sets are {4}, {1, 4}, {1, 2, 4}.

Jinyuan Wang, Table of n, a(n) for n = 1..134
Wikipedia, Geometric mean

Subsets whose mean is an integer are A051293.
Partitions whose geometric mean is an integer are A067539.
Partial sums are A326027.
Strict partitions whose geometric mean is an integer are A326625.
Cf. A005117, A102627, A316413, A326623.

Table[Length[Select[Subsets[Range[n]],MemberQ[#,n]&&IntegerQ[GeometricMean[#]]&]],{n,15}] (* Gus Wiseman, Jul 19 2019 *)

{ A082553(n) = my(m,c=0); if(issquarefree(n),return(1)); m = Set(vector(n-1,i,i)); forprime(p=sqrtint(n)+1,n, m = setminus(m,vector(n\p,i,p*i)); if(Mod(n,p)==0, return(A082553(n\p)) ); ); forvec(v=vector(#m,i,[0,1]), c += ispower(n*factorback(m,v),1+vecsum(v)) ); c; } \\ Max Alekseyev, Aug 31 2013

from sympy import factorint, factorial
def make_product(p, n, k):
    '''
    Find all k-element subsets of {1, ..., n} whose product is p.
    Returns: list of lists
    '''
    if n**k < p:
        return []
    if k == 1:
        return [[p]]
    if p%n == 0:
        l = [s + [n] for s in make_product(p//n, n - 1, k - 1)]
    else:
        l = []
    return l + make_product(p, n - 1, k)
def integral_geometric_mean(n):
    '''
    Find all subsets of {1, ..., n} that contain n and whose
    geometric mean is an integer.
    '''
    f = factorial(n)
    l = [[n]]
    #Find product of distinct prime factors of n
    c = 1
    for p in factorint(n):
        c *= p
    #geometric mean must be a multiple of c
    for gm in range(c, n, c):
        k = 2
        while not (gm**k%n == 0):
            k += 1
        while gm**k <= f:
            l += [s + [n] for s in make_product(gm**k//n, n - 1, k - 1)]
            k += 1
    return l
def A082553(n):
    return len(integral_geometric_mean(n)) # David Wasserman, Aug 02 2019

a(24)-a(62) from Max Alekseyev, Aug 31 2013

a(63)-a(99) from David Wasserman, Aug 02 2019

A326029 Number of strict integer partitions of n whose mean and geometric mean are both integers.

Original entry on oeis.org

0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 3, 1, 1, 1, 1, 3, 1, 2, 1, 3, 1, 1, 2, 3, 1, 3, 1, 1, 3, 6, 1, 3, 1, 2, 1, 1, 1, 3, 1, 6, 1, 5, 1, 2, 2, 2, 4, 3, 1, 9, 1, 1, 3, 1, 1, 4, 1, 4, 2, 6, 1, 6, 1, 3, 7, 4, 2, 5, 1, 10, 1, 3, 1, 9, 3

Offset: 0

Gus Wiseman, Jul 16 2019

nonn

			The a(55) = 2 through a(60) = 9 partitions:
  (55)           (56)         (57)        (58)    (59)  (60)
  (27,16,9,2,1)  (24,18,8,6)  (49,7,1)    (49,9)        (54,6)
                              (27,25,5)   (50,8)        (48,12)
                              (27,18,12)                (27,24,9)
                                                        (27,24,6,2,1)
                                                        (36,12,9,2,1)
                                                        (36,9,6,4,3,2)
                                                        (24,18,9,6,2,1)
                                                        (27,16,9,4,3,1)

Wikipedia, Geometric mean

Partitions with integer mean and geometric mean are A326641.
Strict partitions with integer mean are A102627.
Strict partitions with integer geometric mean are A326625.
Non-constant partitions with integer mean and geometric mean are A326641.
Subsets with integer mean and geometric mean are A326643.
Heinz numbers of partitions with integer mean and geometric mean are A326645.
Cf. A051293, A067538, A067539, A078175, A082553, A316413, A326027, A326623, A326644, A326646, A326647.

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

More terms from Jinyuan Wang, Jun 26 2020

cp's OEIS Frontend

A326647 Number of factorizations of n into factors > 1 with integer average and integer geometric mean.

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A326673 The positions of ones in the reversed binary expansion of n have integer geometric mean.

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A326643 Number of subsets of {1..n} whose mean and geometric mean are both integers.

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Extensions

A326624 Heinz numbers of non-constant integer partitions whose geometric mean is an integer.

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A340606 Numbers whose prime indices (A112798) are all divisors of the number of prime factors (A001222).

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A362559 Number of integer partitions of n whose weighted sum is divisible by n.

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Mathematica

A326672 The positions of ones in the binary expansion of n have integer geometric mean.

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Mathematica

A271654 a(n) = Sum_{k|n} binomial(n-1,k-1).

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PARI

A082553 Number of sets of distinct positive integers whose geometric mean is an integer, the largest integer of a set is n.

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