Composite numbers k with no single digit factors whose factors are all substrings of k: Difference between revisions
Composite numbers k with no single digit factors whose factors are all substrings of k (view source)
Revision as of 08:51, 13 July 2023
, 10 months agoAdd C
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<pre>15317
59177
83731
119911
183347
192413
1819231
2111317
2237411
3129361</pre>
=={{header|C}}==
<syntaxhighlight lang="c">#include <stdio.h>
#include <stdbool.h>
bool is_substring(unsigned n, unsigned k) {
unsigned startMatch = 0;
for (unsigned pfx = k; n > 0; n /= 10) {
if (pfx % 10 == n % 10) {
pfx /= 10;
if (startMatch == 0) startMatch = n;
} else {
pfx = k;
if (startMatch != 0) n = startMatch;
startMatch = 0;
}
if (pfx == 0) return true;
}
return false;
}
bool factors_are_substrings(unsigned n) {
if (n%2==0 || n%3==0 || n%5==0 || n%7==0) return false;
unsigned factor_count = 0;
for (unsigned factor = 11, n_rest = n; factor <= n_rest; factor += 2) {
if (n_rest % factor != 0) continue;
while (n_rest % factor == 0) n_rest /= factor;
if (!is_substring(n, factor)) return false;
factor_count++;
}
return factor_count > 1;
}
int main(void) {
unsigned amount = 10;
for (unsigned n = 11; amount > 0; n += 2) {
if (factors_are_substrings(n)) {
printf("%u\n", n);
amount--;
}
}
return 0;
}</syntaxhighlight>
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<pre>15317
59177
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