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

Terms

a(0) =1a(1) =1a(2) =0a(3) =1a(4) =3a(5) =5a(6) =7a(7) =13a(8) =35a(9) =82a(10) =168a(11) =409a(12) =1035a(13) =2540a(14) =6262a(15) =16068a(16) =41474a(17) =107259a(18) =279256a(19) =736359a(20) =1953946a(21) =5205746a(22) =13938670a(23) =37567522a(24) =101675407a(25) =276158642a(26) =752927255a(27) =2060852216a(28) =5658658210a(29) =15582628517