a(n) = Sum_{k=0..2n} (k+1) * A026568(n, k).

Terms

a(0) =1a(1) =6a(2) =21a(3) =76a(4) =235a(5) =738a(6) =2177a(7) =6424a(8) =18423a(9) =52590a(10) =147917a(11) =413796a(12) =1147523a(13) =3166842a(14) =8689305a(15) =23745584a(16) =64621199a(17) =175277574a(18) =473909989a(19) =1277864060a(20) =3436938267a(21) =9223203858a(22) =24699503281a(23) =66020102472a(24) =176160084775a(25) =469293598878