a(n) = (5*n + 5)*(5*n + 6)*(5*n + 7)/6.

Terms

a(0) =35a(1) =220a(2) =680a(3) =1540a(4) =2925a(5) =4960a(6) =7770a(7) =11480a(8) =16215a(9) =22100a(10) =29260a(11) =37820a(12) =47905a(13) =59640a(14) =73150a(15) =88560a(16) =105995a(17) =125580a(18) =147440a(19) =171700a(20) =198485a(21) =227920a(22) =260130a(23) =295240a(24) =333375a(25) =374660a(26) =419220a(27) =467180a(28) =518665a(29) =573800