a(n) = n*(n-3)*(n^2-7*n+14)/8.

Terms

a(0) =0a(1) =1a(2) =5a(3) =18a(4) =49a(5) =110a(6) =216a(7) =385a(8) =638a(9) =999a(10) =1495a(11) =2156a(12) =3015a(13) =4108a(14) =5474a(15) =7155a(16) =9196a(17) =11645a(18) =14553a(19) =17974a(20) =21965a(21) =26586a(22) =31900a(23) =37973a(24) =44874a(25) =52675a(26) =61451a(27) =71280a(28) =82243a(29) =94424