a(n) = [x^n] Product_{k>=1} 1/(1 - x^(k^2))^n.

Terms

a(0) =1a(1) =1a(2) =3a(3) =10a(4) =39a(5) =151a(6) =588a(7) =2304a(8) =9111a(9) =36307a(10) =145553a(11) =586246a(12) =2370264a(13) =9614242a(14) =39105580a(15) =159444160a(16) =651468967a(17) =2666771488a(18) =10934393619a(19) =44899828056a(20) =184616878289a(21) =760010818689