a(n) = (5*n-7)*(n-1).

Terms

a(0) =0a(1) =3a(2) =16a(3) =39a(4) =72a(5) =115a(6) =168a(7) =231a(8) =304a(9) =387a(10) =480a(11) =583a(12) =696a(13) =819a(14) =952a(15) =1095a(16) =1248a(17) =1411a(18) =1584a(19) =1767a(20) =1960a(21) =2163a(22) =2376a(23) =2599a(24) =2832a(25) =3075a(26) =3328a(27) =3591a(28) =3864a(29) =4147