Expansion of g/(1 - x^4*g), where g = 1+x*g^2 is the g.f. of A000108.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =15a(5) =44a(6) =137a(7) =443a(8) =1473a(9) =4997a(10) =17234a(11) =60244a(12) =212965a(13) =759997a(14) =2734241a(15) =9906337a(16) =36112670a(17) =132361797a(18) =487484793a(19) =1803162895a(20) =6695722220a(21) =24951017572a(22) =93275820198a(23) =349719223200