a(n) = binomial(2 + 2^n,3).

Terms

a(0) =1a(1) =4a(2) =20a(3) =120a(4) =816a(5) =5984a(6) =45760a(7) =357760a(8) =2829056a(9) =22500864a(10) =179481600a(11) =1433753600a(12) =11461636096a(13) =91659526144a(14) =733141975040