OFFSET
1,1
COMMENTS
In most cases S(24*(3*k+1)) == 8*(3*k+1) (mod 24*(3*k+1)).
MATHEMATICA
fu[n_] := fu[n] = Mod[Sum[PowerMod[i + j I, n, n], {i, 0, n - 1}, {j, 0, n - 1}], n]; Select[Range[50], ! fu[24*(3 # +1)] == 8*(3 # +1) &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
José María Grau Ribas, Nov 17 2013
STATUS
approved