Expansion of Product_{k>=1} (1 + k^4*x^k).

Terms

a(0) =1a(1) =1a(2) =16a(3) =97a(4) =337a(5) =2177a(6) =7313a(7) =38529a(8) =108594a(9) =717186a(10) =2053522a(11) =7527458a(12) =30757155a(13) =88042387a(14) =448973459a(15) =1390503396a(16) =4087546309a(17) =12699966117a(18) =49599776261a(19) =124699632310a(20) =608410782855