a(n) = 7*n^2 + 14*n.

Terms

a(0) =21a(1) =56a(2) =105a(3) =168a(4) =245a(5) =336a(6) =441a(7) =560a(8) =693a(9) =840a(10) =1001a(11) =1176a(12) =1365a(13) =1568a(14) =1785a(15) =2016a(16) =2261a(17) =2520a(18) =2793a(19) =3080a(20) =3381a(21) =3696a(22) =4025a(23) =4368a(24) =4725a(25) =5096a(26) =5481a(27) =5880a(28) =6293a(29) =6720