compute 900-841+784-729+...+36-25+16-9+4-1
If I understand your sequence, then this is the "closed form" of the sequence:
a_n = 63 - 4 n
Sum = (59, 55, 51, 47, 43, 39, 35, 31, 27, 23, 19, 15, 11, 7, 3) = 465
