E.g.f. exp(x)*(x^2+x+2)/(1-x).

Terms

a(0) =2a(1) =5a(2) =16a(3) =59a(4) =254a(5) =1297a(6) =7820a(7) =54791a(8) =438394a(9) =3945629a(10) =39456392a(11) =434020435a(12) =5208245366a(13) =67707189929a(14) =947900659204