A022649 Expansion of Product_{m >=1} (1+m*q^m)^21.

1, 21, 252, 2275, 17052, 111594, 657419, 3557256, 17931459, 85093393, 383211885, 1648114587, 6803773998, 27073141326, 104199172863, 389047640905, 1412682672765, 4999550830281, 17277525329491, 58400376126855, 193361098926450, 627924447630011, 2002332877504113

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 0..1000

Programs

Magma

Coefficients(&*[(1+m*x^m)^21:m in [1..40]])[1..40] where x is PolynomialRing(Integers()).1; // G. C. Greubel, Mar 20 2018

Mathematica

With[{nmax=50}, CoefficientList[Series[Product[(1+m*q^m)^21,{m,1,nmax}],{q,0,nmax}],q]] (* G. C. Greubel, Mar 20 2018 *)

PARI

m=50; q='q+O('q^m); Vec(prod(n=1,m,(1+n*q^n)^21)) \\ G. C. Greubel, Mar 20 2018

Extensions

Terms a(19) onward added by G. C. Greubel, Mar 20 2018