G.f.: A(x) = ( Sum_{n>=0} (-4)^n * x^(n^2) )^(-1/2).

Terms

a(0) =1a(1) =2a(2) =6a(3) =20a(4) =62a(5) =204a(6) =684a(7) =2312a(8) =7926a(9) =27436a(10) =95572a(11) =334872a(12) =1178796a(13) =4164984a(14) =14763096a(15) =52471056a(16) =186928422a(17) =667295052a(18) =2386388356a(19) =8547855032a(20) =30661465476a(21) =110125076328a(22) =395989755496