a(n) = (1/6)*(n^3 + 21*n^2 + 74*n + 18).

Terms

a(0) =3a(1) =19a(2) =43a(3) =76a(4) =119a(5) =173a(6) =239a(7) =318a(8) =411a(9) =519a(10) =643a(11) =784a(12) =943a(13) =1121a(14) =1319a(15) =1538a(16) =1779a(17) =2043a(18) =2331a(19) =2644a(20) =2983a(21) =3349a(22) =3743a(23) =4166a(24) =4619a(25) =5103a(26) =5619a(27) =6168a(28) =6751a(29) =7369