a(n) = Sum_{k=0..n} (k+1) * A026648(n,k).

Terms

a(0) =1a(1) =3a(2) =10a(3) =25a(4) =66a(5) =154a(6) =392a(7) =882a(8) =2180a(9) =4796a(10) =11640a(11) =25220a(12) =60424a(13) =129480a(14) =307264a(15) =652936a(16) =1538064a(17) =3247024a(18) =7604000a(19) =15968400a(20) =37217312a(21) =77818016a(22) =180652416a(23) =376359200a(24) =870795328a(25) =1808574912a(26) =4172640640a(27) =8643327040