Partial sums of A056273.

Terms

a(0) =1a(1) =3a(2) =8a(3) =23a(4) =75a(5) =278a(6) =1154a(7) =5265a(8) =25913a(9) =135212a(10) =736704a(11) =4139831a(12) =23767895a(13) =138468210a(14) =814675838a(15) =4824766301a(16) =28699128501a(17) =171207852152