a(n) = T(n,n-3), array T as in A050143.

Terms

a(0) =1a(1) =15a(2) =80a(3) =432a(4) =2352a(5) =12896a(6) =71136a(7) =394400a(8) =2196128a(9) =12273648a(10) =68811184a(11) =386838480a(12) =2179890000a(13) =12309739968a(14) =69641542848a(15) =394643939904