39 lines
875 B
C
39 lines
875 B
C
#include <stdio.h>
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// See https://en.wikipedia.org/wiki/Divisor_function
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unsigned int divisor_count(unsigned int n) {
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unsigned int total = 1;
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// Deal with powers of 2 first
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for (; (n & 1) == 0; n >>= 1) {
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++total;
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}
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// Odd prime factors up to the square root
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for (unsigned int p = 3; p * p <= n; p += 2) {
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unsigned int count = 1;
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for (; n % p == 0; n /= p) {
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++count;
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}
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total *= count;
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}
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// If n > 1 then it's prime
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if (n > 1) {
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total *= 2;
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}
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return total;
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}
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int main() {
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const unsigned int limit = 100;
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unsigned int n;
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printf("Count of divisors for the first %d positive integers:\n", limit);
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for (n = 1; n <= limit; ++n) {
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printf("%3d", divisor_count(n));
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if (n % 20 == 0) {
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printf("\n");
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}
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}
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return 0;
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}
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