G.f.: Sum_{k>=0} (1 + k*x)^k * x^(2*k).

Terms

a(0) =1a(1) =0a(2) =1a(3) =1a(4) =1a(5) =4a(6) =5a(7) =9a(8) =28a(9) =43a(10) =97a(11) =281a(12) =507a(13) =1286a(14) =3666a(15) =7494a(16) =20470a(17) =58725a(18) =132484a(19) =381700a(20) =1113180a(21) =2719887a(22) =8171219a(23) =24337511a(24) =63524916a(25) =197606643a(26) =602261524a(27) =1662206380a(28) =5328738685a(29) =16628469912