Duplicate of A047755.

Terms

a(0) =0a(1) =0a(2) =1a(3) =5a(4) =26a(5) =133a(6) =708a(7) =3861a(8) =21604a(9) =123266a(10) =715221a(11) =4206956a(12) =25032840a(13) =150413348