a(n) = n*(n-1)*(n-2)*(n-3)*(n^2-3*n-2)/48.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =20a(6) =120a(7) =455a(8) =1330a(9) =3276a(10) =7140a(11) =14190a(12) =26235a(13) =45760a(14) =76076a(15) =121485a(16) =187460a(17) =280840a(18) =410040a(19) =585276a(20) =818805a(21) =1125180a(22) =1521520a(23) =2027795a(24) =2667126a(25) =3466100a(26) =4455100a(27) =5668650a(28) =7145775a(29) =8930376