a(n) = T(2n,n+3), T given by A027948.

Terms

a(0) =1a(1) =8a(2) =129a(3) =967a(4) =4950a(5) =20175a(6) =70954a(7) =226007a(8) =672959a(9) =1914166a(10) =5280288a(11) =14275838a(12) =38102976a(13) =100888126a(14) =265838881a(15) =698489013a(16) =1832277574a(17) =4802042229a(18) =12578921258a(19) =32941567397a(20) =86254888591a(21) =225835057708a(22) =591265802288