a(n) = 36*n^2 - 55*n + 21.

Terms

a(0) =2a(1) =55a(2) =180a(3) =377a(4) =646a(5) =987a(6) =1400a(7) =1885a(8) =2442a(9) =3071a(10) =3772a(11) =4545a(12) =5390a(13) =6307a(14) =7296a(15) =8357a(16) =9490a(17) =10695a(18) =11972a(19) =13321a(20) =14742a(21) =16235a(22) =17800a(23) =19437a(24) =21146a(25) =22927a(26) =24780a(27) =26705a(28) =28702a(29) =30771