Wieferich primes: Difference between revisions

=={{header|C#}}==

{{trans|Java}}

<lang csharp>using System;

using System.Collections.Generic;

using System.Linq;

namespace WieferichPrimes {

class Program {

static long ModPow(long @base, long exp, long mod) {

if (mod == 1) {

return 0;

}

long result = 1;

@base %= mod;

for (; exp > 0; exp >>= 1) {

if ((exp & 1) == 1) {

result = (result * @base) % mod;

}

@base = (@base * @base) % mod;

}

return result;

}

static bool[] PrimeSieve(int limit) {

bool[] sieve = Enumerable.Repeat(true, limit).ToArray();

if (limit > 0) {

sieve[0] = false;

}

if (limit > 1) {

sieve[1] = false;

}

for (int i = 4; i < limit; i += 2) {

sieve[i] = false;

}

for (int p = 3; ; p += 2) {

int q = p * p;

if (q >= limit) {

break;

}

if (sieve[p]) {

int inc = 2 * p;

for (; q < limit; q += inc) {

sieve[q] = false;

}

}

}

return sieve;

}

static List<int> WiefreichPrimes(int limit) {

bool[] sieve = PrimeSieve(limit);

List<int> result = new List<int>();

for (int p = 2; p < limit; p++) {

if (sieve[p] && ModPow(2, p - 1, p * p) == 1) {

result.Add(p);

}

}

return result;

}

static void Main() {

const int limit = 5000;

Console.WriteLine("Wieferich primes less that {0}:", limit);

foreach (int p in WiefreichPrimes(limit)) {

Console.WriteLine(p);

}

}

}

}</lang>

{{out}}

<pre>Wieferich primes less that 5000:

1093

3511</pre>