a(n) = n^4 - (n+1)^3.

Terms

a(0) =-1a(1) =-7a(2) =-11a(3) =17a(4) =131a(5) =409a(6) =953a(7) =1889a(8) =3367a(9) =5561a(10) =8669a(11) =12913a(12) =18539a(13) =25817a(14) =35041a(15) =46529a(16) =60623a(17) =77689a(18) =98117a(19) =122321a(20) =150739a(21) =183833a(22) =222089a(23) =266017a(24) =316151a(25) =373049a(26) =437293a(27) =509489a(28) =590267a(29) =680281