a(n) = binomial(n,3)*2^(n-3).

Terms

a(0) =1a(1) =8a(2) =40a(3) =160a(4) =560a(5) =1792a(6) =5376a(7) =15360a(8) =42240a(9) =112640a(10) =292864a(11) =745472a(12) =1863680a(13) =4587520a(14) =11141120a(15) =26738688a(16) =63504384a(17) =149422080a(18) =348651520a(19) =807403520a(20) =1857028096a(21) =4244635648a(22) =9646899200a(23) =21810380800a(24) =49073356800a(25) =109924319232