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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =5a(7) =13a(8) =31a(9) =75a(10) =155a(11) =344a(12) =808a(13) =2019a(14) =5136a(15) =13422a(16) =34720a(17) =91055a(18) =238447a(19) =630753a(20) =1678780a(21) =4502862a(22) =12135507a(23) =32873145a(24) =89324119a(25) =243745113a(26) =667153916a(27) =1832553339a(28) =5048767393a(29) =13950607375