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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =5a(5) =26a(6) =91a(7) =246a(8) =589a(9) =1468a(10) =4226a(11) =13311a(12) =41471a(13) =122864a(14) =351184a(15) =1001876a(16) =2920957a(17) =8698612a(18) =26070130a(19) =77707056a(20) =229959130a(21) =679050870a(22) =2011457295a(23) =5986185690a(24) =17866178695a(25) =53343031301a(26) =159149943668a(27) =474683353849