A002763 Number of bipartite partitions.

4, 11, 26, 52, 98, 171, 289, 467, 737, 1131, 1704, 2515, 3661, 5246, 7430, 10396, 14405, 19760, 26884, 36269, 48583, 64614, 85399, 112170, 146526, 190362, 246099, 316621, 405556, 517224, 657012, 831320, 1048055, 1316611, 1648486, 2057324, 2559719, 3175309

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn

References

• M. S. Cheema and H. Gupta, Tables of Partitions of Gaussian Integers. National Institute of Sciences of India, Mathematical Tables, Vol. 1, New Delhi, 1956, p. 11.
• 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).

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..300
• M. S. Cheema and H. Gupta, Tables of Partitions of Gaussian Integers. National Institute of Sciences of India, Mathematical Tables, Vol. 1, New Delhi, 1956 (Annotated scanned pages from, plus a review)

Crossrefs

Cf. A082775, A129306.

Programs

Maple

with(numtheory):
b:= proc(n, k) option remember;
      `if`(n>k, 0, 1) +`if`(isprime(n), 0,
      add(`if`(d>k, 0, b(n/d, d)), d=divisors(n) minus {1, n}))
    end:
a:= n-> b((45*2^n)$2):
seq(a(n), n=0..50);  # Alois P. Heinz, May 26 2013

Mathematica

b[n_, k_] := b[n, k] = If[n>k, 0, 1] + If[PrimeQ[n], 0, Sum[If[d>k, 0, b[n/d, d]], {d, DeleteCases[Divisors[n], 1|n]}]]; a[n_] := b[45*2^n, 45*2^n]; Table[a[n], {n, 0, 50}] (* Jean-François Alcover, Mar 20 2014, after Alois P. Heinz *)
nmax = 100; CoefficientList[Series[(4 - x - 3*x^2 + x^3) / ((1 - x)^3 * (1 + x)) / Product[1 - x^k, {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Jan 07 2017 *)

Formula

a(n) = a(n-1) + A000041(n) + A000070(n) + A000291(n), for n>0 - Alford Arnold, Dec 10 2007

From Vaclav Kotesovec, Jan 07 2017: (Start)

G.f.: (4 - x - 3*x^2 + x^3) / ((1-x)^3 * (1+x)) * Product_{k>=1} 1/(1-x^k).

a(n) ~ exp(Pi*sqrt(2*n/3)) * 3*sqrt(n)/(2*sqrt(2)*Pi^3).

(End)

Extensions

Extended beyond a(25) by Alois P. Heinz, May 26 2013