Another problem from the Mathematics help desk at Wikipedia: How many ways to write 0 as a sum +- 1^2 +- 2^2 +- 3^2 +- ... +- n^2 ? Here "+-" is "plus or minus". Seems to be 0 for n <= 6, then starting at n=7: 2,2,0,0,2,10,0,0,86,114,... Brendan.