Smarandache-Wellin primes: Difference between revisions
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=={{header|C}}==
{{trans|Wren}}
===Basic===
<syntaxhighlight lang="c">#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <stdint.h>
bool isPrime(uint64_t n) {
if (n < 2) return false;
if (n%2 == 0) return n == 2;
if (n%3 == 0) return n == 3;
uint64_t d = 5;
while (d*d <= n) {
if (n%d == 0) return false;
d += 2;
if (n%d == 0) return false;
d += 4;
}
return true;
}
bool *sieve(int limit) {
int i, p;
limit++;
// True denotes composite, false denotes prime.
bool *c = calloc(limit, sizeof(bool)); // all false by default
c[0] = true;
c[1] = true;
for (i = 4; i < limit; i += 2) c[i] = true;
p = 3; // Start from 3.
while (true) {
int p2 = p * p;
if (p2 >= limit) break;
for (i = p2; i < limit; i += 2 * p) c[i] = true;
while (true) {
p += 2;
if (!c[p]) break;
}
}
return c;
}
int main() {
bool *c = sieve(400);
char sw[100] = "";
char tmp[20];
int swp[3];
int count = 0, p = 1, i;
while (count < 3) {
while (c[++p]);
sprintf(tmp, "%d", p);
strcat(sw, tmp);
int n = atoi(sw);
if (isPrime(n)) swp[count++] = n;
}
printf("The first 3 Smarandache-Wellin primes are:\n");
for (i = 0; i < 3; ++i) printf("%d ", swp[i]);
printf("\n");
int freqs[10] = {0};
uint64_t dswp[3];
count = 0;
p = 1;
while (count < 3) {
while (c[++p]);
sprintf(tmp, "%d", p);
for (i = 0; i < strlen(tmp); ++i) freqs[tmp[i]-48]++;
char dsw[20] = "";
for (i = 0; i < 10; ++i) {
sprintf(tmp, "%d", freqs[i]);
strcat(dsw, tmp);
}
int ix = -1;
for (i = 0; i < strlen(dsw); ++i) {
if (dsw[i] != '0') {
ix = i;
break;
}
}
uint64_t dn = atoll(dsw + ix);
if (isPrime(dn)) dswp[count++] = dn;
}
printf("\nThe first 3 Derived Smarandache-Wellin primes are:\n");
for (i = 0; i < 3; ++i) printf("%ld ", dswp[i]);
printf("\n");
free(c);
return 0;
}</syntaxhighlight>
{{out}}
<pre>
The first 3 Smarandache-Wellin primes are:
2 23 2357
The first 3 Derived Smarandache-Wellin primes are:
4194123321127 547233879626521 547233979727521
</pre>
===Stretch===
{{libheader|GMP}}
<syntaxhighlight lang="c">#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <stdint.h>
#include <gmp.h>
bool *sieve(int limit) {
int i, p;
limit++;
// True denotes composite, false denotes prime.
bool *c = calloc(limit, sizeof(bool)); // all false by default
c[0] = true;
c[1] = true;
for (i = 4; i < limit; i += 2) c[i] = true;
p = 3; // Start from 3.
while (true) {
int p2 = p * p;
if (p2 >= limit) break;
for (i = p2; i < limit; i += 2 * p) c[i] = true;
while (true) {
p += 2;
if (!c[p]) break;
}
}
return c;
}
int main() {
bool *c = sieve(12000);
char sw[6000] = "";
char tmp[20];
int count = 0, p = 1, ix = 0;
mpz_t n;
mpz_init(n);
printf("The 4th to the 8th Smarandache-Wellin primes are:\n");
while (count < 8) {
while (c[++p]);
sprintf(tmp, "%d", p);
strcat(sw, tmp);
mpz_set_str(n, sw, 10);
if (mpz_probab_prime_p(n, 15) > 0) {
count++;
if (count > 3) {
printf("%dth: index %4d digits %4ld last prime %5d\n", count, ix+1, strlen(sw), p);
}
}
ix++;
}
free(c);
return 0;
}</syntaxhighlight>
{{out}}
<pre>
The 4th to the 8th Smarandache-Wellin primes are:
4th: index 128 digits 355 last prime 719
5th: index 174 digits 499 last prime 1033
6th: index 342 digits 1171 last prime 2297
7th: index 435 digits 1543 last prime 3037
8th: index 1429 digits 5719 last prime 11927
</pre>
=={{header|Go}}==
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