G.f. A(x) satisfies: A(x) = 1 + x + x^2 * A(x/(1 - x)) / (1 - x)^2.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =7a(5) =17a(6) =47a(7) =145a(8) =481a(9) =1691a(10) =6295a(11) =24805a(12) =103095a(13) =449805a(14) =2052081a(15) =9762699a(16) =48334855a(17) =248568321a(18) =1325297879a(19) =7312927481a(20) =41694974649a(21) =245288605059