a(n) = 6^n/8 - 4^(n-1) + 2^(n-3).

Terms

a(0) =0a(1) =0a(2) =1a(3) =12a(4) =100a(5) =720a(6) =4816a(7) =30912a(8) =193600a(9) =1194240a(10) =7296256a(11) =44301312a(12) =267904000a(13) =1615810560a(14) =9728413696a(15) =58504691712a(16) =351565004800