a(n) = (n+3)^3 - n^3.

Terms

a(0) =63a(1) =117a(2) =189a(3) =279a(4) =387a(5) =513a(6) =657a(7) =819a(8) =999a(9) =1197a(10) =1413a(11) =1647a(12) =1899a(13) =2169a(14) =2457a(15) =2763a(16) =3087a(17) =3429a(18) =3789a(19) =4167a(20) =4563a(21) =4977a(22) =5409a(23) =5859a(24) =6327a(25) =6813a(26) =7317a(27) =7839a(28) =8379a(29) =8937