n^3 - (n+2)^2.

Terms

a(0) =-4a(1) =-8a(2) =-8a(3) =2a(4) =28a(5) =76a(6) =152a(7) =262a(8) =412a(9) =608a(10) =856a(11) =1162a(12) =1532a(13) =1972a(14) =2488a(15) =3086a(16) =3772a(17) =4552a(18) =5432a(19) =6418a(20) =7516a(21) =8732a(22) =10072a(23) =11542a(24) =13148a(25) =14896a(26) =16792a(27) =18842a(28) =21052a(29) =23428