55 lines
1.5 KiB
C#
55 lines
1.5 KiB
C#
using System;
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namespace AttractiveNumbers {
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class Program {
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const int MAX = 120;
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static bool IsPrime(int n) {
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if (n < 2) return false;
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if (n % 2 == 0) return n == 2;
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if (n % 3 == 0) return n == 3;
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int d = 5;
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while (d * d <= n) {
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if (n % d == 0) return false;
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d += 2;
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if (n % d == 0) return false;
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d += 4;
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}
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return true;
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}
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static int PrimeFactorCount(int n) {
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if (n == 1) return 0;
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if (IsPrime(n)) return 1;
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int count = 0;
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int f = 2;
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while (true) {
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if (n % f == 0) {
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count++;
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n /= f;
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if (n == 1) return count;
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if (IsPrime(n)) f = n;
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} else if (f >= 3) {
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f += 2;
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} else {
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f = 3;
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}
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}
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}
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static void Main(string[] args) {
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Console.WriteLine("The attractive numbers up to and including {0} are:", MAX);
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int i = 1;
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int count = 0;
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while (i <= MAX) {
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int n = PrimeFactorCount(i);
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if (IsPrime(n)) {
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Console.Write("{0,4}", i);
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if (++count % 20 == 0) Console.WriteLine();
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}
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++i;
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}
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Console.WriteLine();
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}
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}
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}
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