Benoît Jubin: > 0 is the sum of (the squares of) its first k divisors for two > different values of k (0 and 1) I can't figure out what this means. If you meant: 0 is the sum of (the squares of) its first 0 divisors for two different values (0 and 1) then I disagree, believing the sum to be a null set for both 0 and 1.