a(n) = 4^(n-4)*(n-1)*(n-2)*(n-3).

Terms

a(0) =6a(1) =96a(2) =960a(3) =7680a(4) =53760a(5) =344064a(6) =2064384a(7) =11796480a(8) =64880640a(9) =346030080a(10) =1799356416a(11) =9160359936a(12) =45801799680a(13) =225485783040