a(n) = T(2n,n+3), T given by A026736.

Terms

a(0) =1a(1) =8a(2) =45a(3) =221a(4) =1016a(5) =4506a(6) =19572a(7) =83950a(8) =357310a(9) =1513513a(10) =6392134a(11) =26948764a(12) =113500985a(13) =477801129a(14) =2011058681a(15) =8464967333a(16) =35637556603a(17) =150075181365a(18) =632191803847