DivisorNear finds a divisor of x near target and if possible within the range [low,high].

DivisorNearLower finds a divisor of x near target and if possible within the range [low,high], and <= isqrt(x).

DivisorNearUpper finds a divisor of x near target and if possible within the range [low,high], and >= isqrt(x).

InitRandom seeds math.rand with crypto/rand (imported as cryptorand), such that future math.rand operations are more or less cryptographically secure.