G.f. satisfies: A(x) = 1 + Sum_{n>=0} 2*x^(n^2)*A(x)^n.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =18a(5) =44a(6) =112a(7) =288a(8) =744a(9) =1938a(10) =5104a(11) =13584a(12) =36456a(13) =98468a(14) =267376a(15) =729488a(16) =1999074a(17) =5500412a(18) =15189636a(19) =42084952a(20) =116949848a(21) =325878288a(22) =910333152a(23) =2548892864a(24) =7152113760a(25) =20108587038a(26) =56641227416a(27) =159820928328