a(n) = (17 - 2*n)*n^2.

Terms

a(0) =0a(1) =15a(2) =52a(3) =99a(4) =144a(5) =175a(6) =180a(7) =147a(8) =64a(9) =-81a(10) =-300a(11) =-605a(12) =-1008a(13) =-1521a(14) =-2156a(15) =-2925a(16) =-3840a(17) =-4913a(18) =-6156a(19) =-7581a(20) =-9200a(21) =-11025a(22) =-13068a(23) =-15341a(24) =-17856a(25) =-20625a(26) =-23660a(27) =-26973a(28) =-30576a(29) =-34481