Task: Strange unique prime triplets
C: #include <stdbool.h>
#include <stdio.h>
#include <string.h>

#define LIMIT 3000

void init_sieve(unsigned char sieve[], int limit) {
    int i, j;

    for (i = 0; i < limit; i++) {
        sieve[i] = 1;
    }
    sieve[0] = 0;
    sieve[1] = 0;

    for (i = 2; i < limit; i++) {
        if (sieve[i]) {
            for (j = i + i; j < limit; j += i) {
                sieve[j] = 0;
            }
        }
    }
}

void strange_unique_prime_triplets(unsigned char sieve[], int limit, bool verbose) {
    int count = 0, sum;
    int i, j, k, n, p;
    int pi, pj, pk;

    n = 0;
    for (i = 0; i < limit; i++) {
        if (sieve[i]) {
            n++;
        }
    }

    if (verbose) {
        printf("Strange unique prime triplets < %d:\n", limit);
    }

    for (i = 0; i + 2 < n; i++) {
        pi = 2;
        p = i;
        while (p > 0) {
            pi++;
            if (sieve[pi]) {
                p--;
            }
        }

        for (j = i + 1; j + 1 < n; j++) {
            pj = pi;
            p = j - i;
            while (p > 0) {
                pj++;
                if (sieve[pj]) {
                    p--;
                }
            }

            for (k = j + 1; k < n; k++) {
                pk = pj;
                p = k - j;
                while (p > 0) {
                    pk++;
                    if (sieve[pk]) {
                        p--;
                    }
                }

                sum = pi + pj + pk;
                if (sum < LIMIT && sieve[sum]) {
                    count++;
                    if (verbose) {
                        printf("%2d + %2d + %2d = %d\n", pi, pj, pk, sum);
                    }
                }
            }
        }
    }

    printf("Count of strange unique prime triplets < %d is %d.\n\n", limit, count);
}

int main() {
    unsigned char sieve[LIMIT];

    init_sieve(sieve, LIMIT);

    strange_unique_prime_triplets(sieve, 30, true);
    strange_unique_prime_triplets(sieve, 1000, false);

    return 0;
}

Go: package main

import "fmt"

func isPrime(n int) bool {
    switch {
    case n < 2:
        return false
    case n%2 == 0:
        return n == 2
    case n%3 == 0:
        return n == 3
    default:
        d := 5
        for d*d <= n {
            if n%d == 0 {
                return false
            }
            d += 2
            if n%d == 0 {
                return false
            }
            d += 4
        }
        return true
    }
}

func commatize(n int) string {
    s := fmt.Sprintf("%d", n)
    if n < 0 {
        s = s[1:]
    }
    le := len(s)
    for i := le - 3; i >= 1; i -= 3 {
        s = s[0:i] + "," + s[i:]
    }
    if n >= 0 {
        return s
    }
    return "-" + s
}

func strangePrimes(n int, countOnly bool) int {
    c := 0
    f := "%2d: %2d + %2d + %2d = %2d\n"
    var s int

    for i := 3; i <= n-4; i += 2 {
        if isPrime(i) {
            for j := i + 2; j <= n-2; j += 2 {
                if isPrime(j) {
                    for k := j + 2; k <= n; k += 2 {
                        if isPrime(k) {
                            s = i + j + k
                            if isPrime(s) {
                                c++
                                if !countOnly {
                                    fmt.Printf(f, c, i, j, k, s)
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    return c
}

func main() {
    fmt.Println("Unique prime triples under 30 which sum to a prime:")
    strangePrimes(29, false)
    cs := commatize(strangePrimes(999, true))
    fmt.Printf("\nThere are %s unique prime triples under 1,000 which sum to a prime.\n", cs)
}