Prime reciprocal sum: Difference between revisions

=={{header|C}}==

{{libheader|GMP}}

{{trans|Wren}}

<syntaxhighlight lang="c">#include <stdio.h>

#include <stdbool.h>

#include <string.h>

#include <gmp.h>

void abbreviate(char a[], const char *s) {

size_t len = strlen(s);

if (len < 40) {

strcpy(a, s);

return;

}

strncpy(a, s, 20);

strcpy(a + 20, "...");

strncpy(a + 23, s + len - 20, 21);

}

int main() {

mpq_t q, r, s, u;

mpz_t p, t;

int count = 0, limit = 16;

size_t len;

bool isInteger;

char *ps, a[44];

mpq_inits(q, r, s, u, NULL);

mpq_set_ui(u, 1, 1);

mpz_inits(p, t, NULL);

printf("First %d elements of the sequence:\n", limit);

while (count < limit) {

mpq_sub(q, u, s);

mpq_inv(q, q);

mpq_get_den(t, q);

isInteger = !mpz_cmp_ui(t, 1);

mpz_set_q(p, q);

if (!isInteger) mpz_add_ui(p, p, 1);

mpz_nextprime(p, p);

++count;

ps = mpz_get_str(NULL, 10, p);

len = strlen(ps);

if (len <= 40) {

printf("%2d: %s\n", count, ps);

} else {

abbreviate(a, ps);

printf("%2d: %s (digits: %ld)\n", count, a, len);

}

mpq_set_z(r, p);

mpq_inv(r, r);

mpq_add(s, s, r);

}

mpq_clears(q, r, s, u, NULL);

mpz_clears(p, t, NULL);

return 0;

}</syntaxhighlight>

{{out}}

<pre>

First 16 elements of the sequence:

1: 2

2: 3

3: 7

4: 43

5: 1811

6: 654149

7: 27082315109

8: 153694141992520880899

9: 337110658273917297268061074384231117039

10: 84241975970641143191...13803869133407474043 (digits: 76)

11: 20300753813848234767...91313959045797597991 (digits: 150)

12: 20323705381471272842...21649394434192763213 (digits: 297)

13: 12748246592672078196...20708715953110886963 (digits: 592)

14: 46749025165138838243...65355869250350888941 (digits: 1180)

15: 11390125639471674628...31060548964273180103 (digits: 2358)

16: 36961763505630520555...02467094377885929191 (digits: 4711)

</pre>