Nice primes: Difference between revisions
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Nice primes 500-1000: 33
</pre>
=={{header|C}}==
{{trans|C++}}
<lang c>#include <stdbool.h>
#include <stdio.h>
bool is_prime(unsigned int n) {
if (n < 2) {
return false;
}
if (n % 2 == 0) {
return n == 2;
}
if (n % 3 == 0) {
return n == 3;
}
for (unsigned int p = 5; p * p <= n; p += 4) {
if (n % p == 0) {
return false;
}
p += 2;
if (n % p == 0) {
return false;
}
}
return true;
}
unsigned int digital_root(unsigned int n) {
return n == 0 ? 0 : 1 + (n - 1) % 9;
}
int main() {
const unsigned int from = 500, to = 1000;
unsigned int count = 0;
unsigned int n;
printf("Nice primes between %d and %d:\n", from, to);
for (n = from; n < to; ++n) {
if (is_prime(digital_root(n)) && is_prime(n)) {
++count;
//std::cout << n << (count % 10 == 0 ? '\n' : ' ');
printf("%d", n);
if (count % 10 == 0) {
putc('\n', stdout);
} else {
putc(' ', stdout);
}
}
}
printf("\n%d nice primes found.\n", count);
return 0;
}</lang>
{{out}}
<pre>Nice primes between 500 and 1000:
509 547 563 569 587 599 601 617 619 641
653 659 673 677 691 709 727 743 761 797
821 839 853 857 887 907 911 929 941 947
977 983 997
33 nice primes found.</pre>
=={{header|C++}}==
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