Partial sums of A000262.

Terms

a(0) =1a(1) =2a(2) =5a(3) =18a(4) =91a(5) =592a(6) =4643a(7) =42276a(8) =436629a(9) =5033182a(10) =63974273a(11) =888047414a(12) =13358209647a(13) =216334610860