a(n) = 2^n*(2^n - 1)*(2^n - 2)/6.

Terms

a(0) =0a(1) =0a(2) =4a(3) =56a(4) =560a(5) =4960a(6) =41664a(7) =341376a(8) =2763520a(9) =22238720a(10) =178433024a(11) =1429559296a(12) =11444858880a(13) =91592417280a(14) =732873539584