31 May
2014
31 May
'14
1:52 a.m.
with CarmichaelQ (fairly simple), and three special cases, Block[{a = 15485857, b = 29462131}, Reap[Do[If[! PrimeQ[k] && ! CarmichaelQ[k] && Divisible[ PowerMod[a + b, k, k] - PowerMod[a, k, k] - PowerMod[b, k, k], k], Sow[k]], {k, 2, 117568}]]] {Null, {{56033, 73633, 93961, 104653}}} There may well be superior and smaller a and b. And almost certainly superior larger ones. But I don't have a good way to look for them. --rwg