Task: Long primes
C: #include <stdio.h>
#include <stdlib.h>
 
#define TRUE 1
#define FALSE 0
 
typedef int bool;
 
void sieve(int limit, int primes[], int *count) {
    bool *c = calloc(limit + 1, sizeof(bool)); 
    
    int i, p = 3, p2, n = 0;
    p2 = p * p;
    while (p2 <= limit) {
        for (i = p2; i <= limit; i += 2 * p) 
            c[i] = TRUE;
        do {
            p += 2;
        } while (c[p]);
        p2 = p * p;
    }
    for (i = 3; i <= limit; i += 2) {
        if (!c[i]) primes[n++] = i;
    }
    *count = n;
    free(c);
}
 

int findPeriod(int n) {
    int i, r = 1, rr, period = 0;
    for (i = 1; i <= n + 1; ++i) {
        r = (10 * r) % n;
    }
    rr = r;
    do {
        r = (10 * r) % n;
        period++;
    } while (r != rr);
    return period;
}
 
int main() {
    int i, prime, count = 0, index = 0, primeCount, longCount = 0, numberCount;
    int *primes, *longPrimes, *totals;
    int numbers[] = {500, 1000, 2000, 4000, 8000, 16000, 32000, 64000};
     
    primes = calloc(6500, sizeof(int));
    numberCount = sizeof(numbers) / sizeof(int);
    totals = calloc(numberCount, sizeof(int));
    sieve(64000, primes, &primeCount);
    longPrimes = calloc(primeCount, sizeof(int)); 
    
    for (i = 0; i < primeCount; ++i) {
        prime = primes[i];
        if (findPeriod(prime) == prime - 1) {
            longPrimes[longCount++] = prime;
        }
    }
    for (i = 0; i < longCount; ++i, ++count) {
        if (longPrimes[i] > numbers[index]) {
            totals[index++] = count;
        }
    }
    totals[numberCount - 1] = count;
    printf("The long primes up to %d are:\n", numbers[0]);
    printf("[");
    for (i = 0; i < totals[0]; ++i) {
        printf("%d ", longPrimes[i]);
    }
    printf("\b]\n");
 
    printf("\nThe number of long primes up to:\n");
    for (i = 0; i < 8; ++i) {
        printf("  %5d is %d\n", numbers[i], totals[i]);
    }
    free(totals);
    free(longPrimes);
    free(primes);
    return 0;
}

Go: package main
 
import "fmt"
 
func sieve(limit int) []int {
    var primes []int
    c := make([]bool, limit + 1) 
    
    p := 3
    p2 := p * p
    for p2 <= limit {
        for i := p2; i <= limit; i += 2 * p {
            c[i] = true
        }
        for ok := true; ok; ok = c[p] {
            p += 2
        }
        p2 = p * p
    }
    for i := 3; i <= limit; i += 2 {
        if !c[i] {
            primes = append(primes, i)
        }
    }
    return primes
}
 

func findPeriod(n int) int {
    r := 1
    for i := 1; i <= n + 1; i++ {
        r = (10 * r) % n
    }
    rr := r
    period := 0
    for ok := true; ok; ok = r != rr {
        r = (10 * r) % n
        period++
    }
    return period
}
 
func main() {
    primes := sieve(64000)
    var longPrimes []int
    for _, prime := range primes {
        if findPeriod(prime) == prime - 1 {
            longPrimes = append(longPrimes, prime)
        }
    }
    numbers := []int{500, 1000, 2000, 4000, 8000, 16000, 32000, 64000}
    index := 0
    count := 0
    totals := make([]int, len(numbers))
    for _, longPrime := range longPrimes {
        if longPrime > numbers[index] {
            totals[index] = count
            index++
        }
        count++
    }
    totals[len(numbers)-1] = count
    fmt.Println("The long primes up to", numbers[0], "are: ")
    fmt.Println(longPrimes[:totals[0]])
 
    fmt.Println("\nThe number of long primes up to: ")
    for i, total := range totals {
        fmt.Printf("  %5d is %d\n", numbers[i], total)
    }
}