a(n) = n^3 - (3*(n+3))^2.

Terms

a(0) =-81a(1) =-143a(2) =-217a(3) =-297a(4) =-377a(5) =-451a(6) =-513a(7) =-557a(8) =-577a(9) =-567a(10) =-521a(11) =-433a(12) =-297a(13) =-107a(14) =143a(15) =459a(16) =847a(17) =1313a(18) =1863a(19) =2503a(20) =3239a(21) =4077a(22) =5023a(23) =6083a(24) =7263a(25) =8569a(26) =10007a(27) =11583a(28) =13303a(29) =15173