a(n) = (n^7 - 21*n^3 + 20*n)/210.

Terms

a(0) =0a(1) =0a(2) =0a(3) =8a(4) =72a(5) =360a(6) =1312a(7) =3888a(8) =9936a(9) =22704a(10) =47520a(11) =92664a(12) =170456a(13) =298584a(14) =501696a(15) =813280a(16) =1277856a(17) =1953504a(18) =2914752a(19) =4255848a(20) =6094440a(21) =8575688a(22) =11876832a(23) =16212240a(24) =21838960a(25) =29062800a(26) =38244960a(27) =49809240a(28) =64249848a(29) =82139832