a(n) = T(2*n, n+4), T given by A027935.

Terms

a(0) =1a(1) =46a(2) =551a(3) =3785a(4) =18955a(5) =77533a(6) =276408a(7) =895103a(8) =2708322a(9) =7811510a(10) =21791338a(11) =59419294a(12) =159571139a(13) =424302452a(14) =1121168305a(15) =2951121095a(16) =7749900701a(17) =20324325571a(18) =53259796514a(19) =139506540045a(20) =365330860180a(21) =956582678652