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

Terms

a(0) =1a(1) =2a(2) =10a(3) =36a(4) =166a(5) =556a(6) =2724a(7) =9000a(8) =41542a(9) =153164a(10) =657644a(11) =2325816a(12) =11020508a(13) =38006264a(14) =164662664a(15) =634362320a(16) =2695771462a(17) =9775537676a(18) =43527018396a(19) =156855914904a(20) =687387270260