a(n) is the constant term in expansion of Product_{k=1..n} (x^(k^3) + 1 + 1/x^(k^3)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =3a(7) =3a(8) =5a(9) =17a(10) =31a(11) =61a(12) =139a(13) =309a(14) =701a(15) =1651a(16) =3849a(17) =8929a(18) =22295a(19) =53777a(20) =131025a(21) =335619a(22) =837999a(23) =2107947a(24) =5484373a(25) =14071891a(26) =36275323a(27) =95881995a(28) =250956301a(29) =659257445