a(n) = n*(n + 7)*(n + 14)/6.

Terms

a(0) =0a(1) =20a(2) =48a(3) =85a(4) =132a(5) =190a(6) =260a(7) =343a(8) =440a(9) =552a(10) =680a(11) =825a(12) =988a(13) =1170a(14) =1372a(15) =1595a(16) =1840a(17) =2108a(18) =2400a(19) =2717a(20) =3060a(21) =3430a(22) =3828a(23) =4255a(24) =4712a(25) =5200a(26) =5720a(27) =6273a(28) =6860a(29) =7482