a(n) = T(2*n, n+2), T given by A026998.

Terms

a(0) =1a(1) =26a(2) =174a(3) =743a(4) =2552a(5) =7784a(6) =22193a(7) =60882a(8) =163430a(9) =433495a(10) =1142496a(11) =3001056a(12) =7869649a(13) =20619098a(14) =54001422a(15) =141401879a(16) =370224248a(17) =969294632a(18) =2537687585a(19) =6643800690a(20) =17393752166a(21) =45537499111a(22) =119218794624a(23) =312118940928a(24) =817138091617