Data commit

Task/Long-primes/C-sharp/long-primes.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+public static class LongPrimes
+{
+    public static void Main() {
+        var primes = SomePrimeGenerator.Primes(64000).Skip(1).Where(p => Period(p) == p - 1).Append(99999);
+        Console.WriteLine(string.Join(" ", primes.TakeWhile(p => p <= 500)));
+        int count = 0, limit = 500;
+        foreach (int prime in primes) {
+            if (prime > limit) {
+                Console.WriteLine($"There are {count} long primes below {limit}");
+                limit *= 2;
+            }
+            count++;
+        }
+
+        int Period(int n) {
+            int r = 1, rr;
+            for (int i = 0; i <= n; i++) r = 10 * r % n;
+            rr = r;
+            for (int period = 1;; period++) {
+                r = (10 * r) % n;
+                if (r == rr) return period;
+            }
+        }
+    }
+
+}
+
+static class SomePrimeGenerator {
+
+    public static IEnumerable<int> Primes(int lim) {
+        bool [] flags = new bool[lim + 1]; int j = 2;
+        for (int d = 3, sq = 4; sq <= lim; j++, sq += d += 2)
+            if (!flags[j]) {
+                yield return j; for (int k = sq; k <= lim; k += j)
+                    flags[k] = true;
+            }
+        for (; j<= lim; j++) if (!flags[j]) yield return j;
+    }
+}