a(n) = 81*n^2 - 69*n + 24.

Terms

a(0) =24a(1) =36a(2) =210a(3) =546a(4) =1044a(5) =1704a(6) =2526a(7) =3510a(8) =4656a(9) =5964a(10) =7434a(11) =9066a(12) =10860a(13) =12816a(14) =14934a(15) =17214a(16) =19656a(17) =22260a(18) =25026a(19) =27954a(20) =31044a(21) =34296a(22) =37710a(23) =41286a(24) =45024a(25) =48924a(26) =52986a(27) =57210a(28) =61596a(29) =66144