G.f.: A(x) = 1/(1 - 2*x - 7*x^2 - 2*x^3 + x^4).

Terms

a(0) =1a(1) =2a(2) =11a(3) =38a(4) =156a(5) =598a(6) =2353a(7) =9166a(8) =35843a(9) =139956a(10) =546792a(11) =2135796a(12) =8343205a(13) =32590610a(14) =127308455a(15) =497301794a(16) =1942600788a(17) =7588340434a(18) =29642181517a(19) =115790645854a(20) =452310642407