G.f.: 1/(1 - 3 x - 3 x^2 + 4 x^3 + x^4 - x^5).

Terms

a(0) =1a(1) =3a(2) =12a(3) =41a(4) =146a(5) =511a(6) =1798a(7) =6314a(8) =22187a(9) =77946a(10) =273856a(11) =962142a(12) =3380337a(13) =11876254a(14) =41725295a(15) =146595013a(16) =515037713a(17) =1809501081a(18) =6357387289a(19) =22335644540a(20) =78472648463a(21) =275700866485a(22) =968630080476