G.f. A(x) satisfies: A(x) = 1 + x + x^2 * A(x/(1 - x)) / (1 - x)^4.

Terms

a(0) =1a(1) =1a(2) =1a(3) =5a(4) =16a(5) =46a(6) =142a(7) =496a(8) =1888a(9) =7538a(10) =31291a(11) =135739a(12) =617461a(13) =2939215a(14) =14575027a(15) =75014471a(16) =399901294a(17) =2205630124a(18) =12572140372a(19) =73961880118a(20) =448447331338