Variant of A061417.

Terms

a(0) =1a(1) =2a(2) =4a(3) =11a(4) =28a(5) =152a(6) =726a(7) =5268a(8) =40438a(9) =365944a(10) =3628810a(11) =39974466a(12) =479001612a(13) =6228256404a(14) =87178339984