A026832 -id:A026832 - cp's OEIS frontend

A067659 Number of partitions of n into distinct parts such that number of parts is odd.

0, 1, 1, 1, 1, 1, 2, 2, 3, 4, 5, 6, 8, 9, 11, 14, 16, 19, 23, 27, 32, 38, 44, 52, 61, 71, 82, 96, 111, 128, 148, 170, 195, 224, 256, 293, 334, 380, 432, 491, 557, 630, 713, 805, 908, 1024, 1152, 1295, 1455, 1632, 1829, 2048, 2291, 2560, 2859, 3189, 3554, 3958, 4404

Offset: 0

Naohiro Nomoto, Feb 23 2002

Ramanujan theta functions: phi(q) := Sum_{k=-oo..oo} q^(k^2) (A000122), chi(q) := Prod_{k>=0} (1+q^(2k+1)) (A000700).

			From _Gus Wiseman_, Jan 09 2021: (Start)
The a(5) = 1 through a(15) = 14 partitions (A-F = 10..15):
  5   6     7     8     9     A     B     C     D     E     F
      321   421   431   432   532   542   543   643   653   654
                  521   531   541   632   642   652   743   753
                        621   631   641   651   742   752   762
                              721   731   732   751   761   843
                                    821   741   832   842   852
                                          831   841   851   861
                                          921   931   932   942
                                                A21   941   951
                                                      A31   A32
                                                      B21   A41
                                                            B31
                                                            C21
                                                            54321
(End)

Alois P. Heinz, Table of n, a(n) for n = 0..1000
Joerg Arndt, Matters Computational (The Fxtbook), end of section 16.4.2 "Partitions into distinct parts", pp.348ff
Mircea Merca, Combinatorial interpretations of a recent convolution for the number of divisors of a positive integer, Journal of Number Theory, Volume 160 (March 2016), Pages 60-75, function q_o(n).
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

Dominates A000009.
Numbers with these strict partitions as binary indices are A000069.
The non-strict version is A027193.
The Heinz numbers of these partitions are A030059.
The even version is A067661.
The version for rank is A117193, with non-strict version A101707.
The ordered version is A332304, with non-strict version A166444.
Other cases of odd length:
- A024429 counts set partitions of odd length.
- A089677 counts ordered set partitions of odd length.
- A174726 counts ordered factorizations of odd length.
- A339890 counts factorizations of odd length.
A008289 counts strict partitions by sum and length.
A026804 counts partitions whose least part is odd, with strict case A026832.
Cf. A000700, A027187, A030229, A117192, A332305.

b:= proc(n, i, t) option remember; `if`(n>i*(i+1)/2, 0,
      `if`(n=0, t, add(b(n-i*j, i-1, abs(t-j)), j=0..min(n/i, 1))))
    end:
a:= n-> b(n$2, 0):
seq(a(n), n=0..80);  # Alois P. Heinz, Apr 01 2014

b[n_, i_, t_] := b[n, i, t] = If[n > i*(i + 1)/2, 0, If[n == 0, t, Sum[b[n - i*j, i - 1, Abs[t - j]], {j, 0, Min[n/i, 1]}]]]; a[n_] := b[n, n, 0]; Table[a[n], {n, 0, 80}] (* Jean-François Alcover, Jan 16 2015, after Alois P. Heinz *)
CoefficientList[Normal[Series[(QPochhammer[-x, x]-QPochhammer[x])/2, {x, 0, 100}]], x] (* Andrey Zabolotskiy, Apr 12 2017 *)
Table[Length[Select[IntegerPartitions[n],UnsameQ@@#&&OddQ[Length[#]]&]],{n,0,30}] (* Gus Wiseman, Jan 09 2021 *)

{a(n)=local(A); if(n<0, 0, A=x*O(x^n); polcoeff( (eta(x^2+A)/eta(x+A) - eta(x+A))/2, n))} /* Michael Somos, Feb 14 2006 */

N=66;  q='q+O('q^N);  S=1+2*sqrtint(N);
gf=sum(n=1,S, (n%2!=0) * q^(n*(n+1)/2) / prod(k=1,n, 1-q^k ) );
concat( [0], Vec(gf) )  /* Joerg Arndt, Oct 20 2012 */

N=66;  q='q+O('q^N);  S=1+sqrtint(N);
gf=sum(n=1, S, q^(2*n^2-n) / prod(k=1, 2*n-1, 1-q^k ) );
concat( [0], Vec(gf) )  \\ Joerg Arndt, Apr 01 2014

For g.f. see under A067661.
a(n) = (A000009(n)-A010815(n))/2. - Vladeta Jovovic, Feb 24 2002
Expansion of (1-phi(-q))/(2*chi(-q)) in powers of q where phi(),chi() are Ramanujan theta functions. - Michael Somos, Feb 14 2006
G.f.: sum(n>=1, q^(2*n^2-n) / prod(k=1..2*n-1, 1-q^k ) ). [Joerg Arndt, Apr 01 2014]
a(n) = A067661(n) - A010815(n). - Andrey Zabolotskiy, Apr 12 2017
A000009(n) = a(n) + A067661(n). - Gus Wiseman, Jan 09 2021

A092265 Sum of smallest parts of all partitions of n into distinct parts.

Original entry on oeis.org

1, 2, 4, 5, 8, 10, 14, 16, 23, 26, 34, 40, 50, 58, 74, 83, 102, 120, 142, 164, 198, 226, 266, 308, 359, 412, 482, 548, 634, 730, 834, 950, 1094, 1240, 1416, 1609, 1826, 2068, 2350, 2648, 2994, 3382, 3806, 4280, 4826, 5408, 6070, 6806, 7619, 8522, 9534, 10632

Offset: 1

Vladeta Jovovic, Feb 14 2004

Alois P. Heinz, Table of n, a(n) for n = 1..10000

Cf. A046746, A005895, A006128, A092269, A092319, A092316, A034296, A237665.

Cf. A026832, A336902, A336903.

b:= proc(n, i) option remember; `if`(n=0, 1,
     `if`(i>n, 0, b(n,i+1)+b(n-i, i+1)))
    end:
a:= n-> add(j*b(n-j, j+1), j=1..n):
seq(a(n), n=1..80);  # Alois P. Heinz, Feb 03 2016

b[n_, i_] := b[n, i] = If[n == 0, 1, If[i > n, 0, b[n, i + 1] + b[n - i, i + 1]]]; a[n_] := Sum[j*b[n - j, j + 1], {j, 1, n}]; Table[a[n], {n, 1, 80}] (* Jean-François Alcover, Jan 21 2017, after Alois P. Heinz *)

G.f.: Sum_{n >= 1} (-1 + Product_{k >= n} 1 + x^k).
G.f.: Sum_{n >= 1} n*x^n*Product_{k >= n+1} (1 + x^k). - Joerg Arndt, Jan 29 2011
G.f.: Sum_{k >= 1} x^(k*(k+1)/2)/(1 - x^k)/Product_{i = 1..k} (1 - x^i). - Vladeta Jovovic, Aug 10 2004
Conjecture: a(n) = A034296(n) + A237665(n+1). - George Beck, May 06 2017
a(n) ~ exp(Pi*sqrt(n/3)) / (2 * 3^(1/4) * n^(3/4)). - Vaclav Kotesovec, May 20 2018

More terms from Pab Ter (pabrlos(AT)yahoo.com), May 25 2004

A097042 G.f. = (1 + 4 * g.f. for A096661)/(1 + 2 Sum_{m>=1} (-1)^m*q^(m^2)).

Original entry on oeis.org

1, 2, 0, 4, 2, 4, 4, 8, 8, 10, 12, 16, 20, 24, 28, 36, 42, 48, 60, 72, 84, 100, 116, 136, 160, 186, 216, 252, 292, 336, 388, 448, 512, 588, 672, 768, 878, 1000, 1136, 1292, 1464, 1656, 1876, 2120, 2388, 2696, 3032, 3408, 3832, 4298, 4816, 5396, 6036, 6744, 7532, 8404

Offset: 0

N. J. A. Sloane, Sep 15 2004

nonn

a(0) = 1; for n>0, a(n) = 2*A026832(n) (i.e., essentially Fine's numbers L(n) multiplied by 2).

The number of odd-even overpartitions of n: an odd-even overpartition of n is an overpartition of n with the smallest part odd and such that the difference between successive parts is odd if the smaller part is nonoverlined and even otherwise - see Yang 2017. - Peter Bala, Mar 29 2017

N. J. Fine, Basic Hypergeometric Series and Applications, Amer. Math. Soc., 1988; p. 56, Eq. (26.28).

Vaclav Kotesovec, Table of n, a(n) for n = 0..1000
Min-Joo Jang, Asymptotic behavior of odd-even partitions, arXiv:1703.01837v1 [math.NT], 2017.

Cf. A096661, A026832, A179049.

nmax = 60; Flatten[{1, Rest[CoefficientList[Series[2*Sum[x^(2*k - 1) QPochhammer[-x^(2*k), x], {k, nmax}], {x, 0, nmax}], x]]}] (* Vaclav Kotesovec, Mar 28 2017 *)

a(n) ~ 1/(3^(5/4)*n^(3/4))*exp(Pi*sqrt(n/3)) [Jang 2017]. - Peter Bala, Mar 29 2017

Conjectural g.f.: 1 + 2*Sum_{n >= 1} q^(n*(n+1)/2)/( (1 + q^n) * Product_{k = 1..n} 1 - q^k ). - Peter Bala, Feb 19 2021

Name corrected by Peter Bala, Feb 19 2021

A026833 Number of partitions of n into distinct parts, the least being even.

Original entry on oeis.org

0, 0, 1, 0, 1, 1, 2, 1, 2, 3, 4, 4, 5, 6, 8, 9, 11, 14, 16, 18, 22, 26, 31, 36, 42, 49, 57, 66, 76, 88, 102, 116, 134, 154, 176, 201, 229, 260, 296, 336, 381, 432, 488, 550, 622, 700, 788, 886, 994, 1115, 1250, 1399, 1564, 1748, 1952, 2176, 2426, 2701, 3004

Offset: 0

Clark Kimberling

nonn

Also number of partitions of n such that if k is the largest part, then k occurs an even number of times and each of the numbers 1,2,...,k-1 occurs at least once. Example: a(10)=4 because we have [3,3,2,1,1], [2,2,2,2,1,1], [2,2,1,1,1,1,1,1] and [1,1,1,1,1,1,1,1,1,1]. - Emeric Deutsch, Mar 30 2006

			a(10)=4 because we have [10], [8,2], [6,4] and [5,3,2].

Alois P. Heinz, Table of n, a(n) for n = 0..10000

Cf. A026832.

g:=sum(x^(2*k)*product(1+x^j, j=2*k+1..60), k=1..60): gser:=series(g, x=0, 58): seq(coeff(gser, x, n), n=0..55); # Emeric Deutsch, Mar 30 2006
# second Maple program:
b:= proc(n, i) option remember; `if`(i*(i+1)/2-1 b(n$2):
seq(a(n), n=0..60);  # Alois P. Heinz, Feb 01 2019

b[n_, i_] := b[n, i] = If[i*(i+1)/2-1 < n, 0, b[n, i-1] + If[i == n && EvenQ[i], 1, 0]+If[i < n, b[n-i, Min[n-i, i-1]], 0]];
a[n_] := b[n, n];
Table[a[n], {n, 0, 60}] (* Jean-François Alcover, May 16 2025, after Alois P. Heinz *)

G.f.: Sum_{k>=2} ((-1)^k*(-1+Product_{i>=k} (1+x^i))). - Vladeta Jovovic, Aug 26 2003
G.f.: Sum_{k>=1} x^(2k)*Product_{j>=2k+1} (1+x^j).
G.f.: Sum_{k>=1} x^(k*(k+3)/2)/((1+x^k)*Product_{j=1..k} (1-x^j)). - Emeric Deutsch, Mar 30 2006
a(n) ~ exp(Pi*sqrt(n/3)) / (4 * 3^(5/4) * n^(3/4)). - Vaclav Kotesovec, Jun 09 2019

a(0)=0 prepended by Alois P. Heinz, Feb 01 2019

A027347 Number of partitions of n into distinct odd parts, the least being congruent to 1 mod 4.

Original entry on oeis.org

1, 0, 0, 1, 1, 1, 0, 1, 2, 1, 1, 2, 3, 2, 2, 3, 4, 3, 3, 5, 6, 6, 5, 7, 9, 8, 8, 11, 12, 12, 12, 15, 18, 17, 18, 22, 25, 25, 26, 30, 34, 34, 36, 42, 47, 48, 50, 57, 64, 65, 69, 78, 85, 89, 93, 104, 114, 118, 125, 139, 151, 157, 166, 183, 198, 207, 219, 240

Offset: 1

Clark Kimberling

Cf. A026832.

G := add( q^(4*n+1)*mul( 1 + q^(2*k+1), k = 2*n+1..50 ), n = 0..25 ):
S := series(G, q, 101):
seq(coeff(S, q, j), j = 1..100); # Peter Bala, Jan 31 2021

From Peter Bala, Jan 31 2021: (Start)
G.f.: A(q) = Sum_{n >= 0} q^(4*n+1) * Product_{k >= 2*n+1} 1 + q^(2*k+1).
A(q) = Limit_{N -> oo} Sum_{n = 0..2*N+1} (-1)^n * Product_{k = n..2*N+1} 1 + q^(2*k+1) = Limit_{N -> oo} Sum_{n = 0..2*N+1} (-1)^n * Product_{k >= n} 1 + q^(2*k+1). (End)

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A067659 Number of partitions of n into distinct parts such that number of parts is odd.

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A092265 Sum of smallest parts of all partitions of n into distinct parts.

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A097042 G.f. = (1 + 4 * g.f. for A096661)/(1 + 2 Sum_{m>=1} (-1)^m*q^(m^2)).

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A026833 Number of partitions of n into distinct parts, the least being even.

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A027347 Number of partitions of n into distinct odd parts, the least being congruent to 1 mod 4.

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