Sum_{k=0..n^2} (k^2 - n^2)/n.

Terms

a(0) =-1a(1) =5a(2) =65a(3) =306a(4) =975a(5) =2479a(6) =5425a(7) =10660a(8) =19311a(9) =32825a(10) =53009a(11) =82070a(12) =122655a(13) =177891a(14) =251425a(15) =347464a(16) =470815a(17) =626925a(18) =821921a(19) =1062650a(20) =1356719a(21) =1712535a(22) =2139345a(23) =2647276a(24) =3247375a(25) =3951649a(26) =4773105a(27) =5725790a(28) =6824831a(29) =8086475