Task: Humble numbers
C++: #include <iomanip>
#include <iostream>
#include <map>
#include <sstream>

bool isHumble(int i) {
    if (i <= 1) return true;
    if (i % 2 == 0) return isHumble(i / 2);
    if (i % 3 == 0) return isHumble(i / 3);
    if (i % 5 == 0) return isHumble(i / 5);
    if (i % 7 == 0) return isHumble(i / 7);
    return false;
}

auto toString(int n) {
    std::stringstream ss;
    ss << n;
    return ss.str();
}

int main() {
    auto limit = SHRT_MAX;
    std::map<int, int> humble;
    auto count = 0;
    auto num = 1;

    while (count < limit) {
        if (isHumble(num)) {
            auto str = toString(num);
            auto len = str.length();
            auto it = humble.find(len);

            if (it != humble.end()) {
                it->second++;
            } else {
                humble[len] = 1;
            }

            if (count < 50) std::cout << num << ' ';
            count++;
        }
        num++;
    }
    std::cout << "\n\n";

    std::cout << "Of the first " << count << " humble numbers:\n";
    num = 1;
    while (num < humble.size() - 1) {
        auto it = humble.find(num);
        if (it != humble.end()) {
            auto c = *it;
            std::cout << std::setw(5) << c.second << " have " << std::setw(2) << num << " digits\n";
            num++;
        } else {
            break;
        }
    }

    return 0;
}

Go: package main

import (
    "fmt"
    "math/big"
)

var (
    one   = new(big.Int).SetUint64(1)
    two   = new(big.Int).SetUint64(2)
    three = new(big.Int).SetUint64(3)
    five  = new(big.Int).SetUint64(5)
    seven = new(big.Int).SetUint64(7)
    ten   = new(big.Int).SetUint64(10)
)

func min(a, b *big.Int) *big.Int {
    if a.Cmp(b) < 0 {
        return a
    }
    return b
}

func humble(n int) []*big.Int {
    h := make([]*big.Int, n)
    h[0] = new(big.Int).Set(one)
    next2, next3 := new(big.Int).Set(two), new(big.Int).Set(three)
    next5, next7 := new(big.Int).Set(five), new(big.Int).Set(seven)
    var i, j, k, l int
    for m := 1; m < len(h); m++ {
        h[m] = new(big.Int).Set(min(next2, min(next3, min(next5, next7))))
        if h[m].Cmp(next2) == 0 {
            i++
            next2.Mul(two, h[i])
        }
        if h[m].Cmp(next3) == 0 {
            j++
            next3.Mul(three, h[j])
        }
        if h[m].Cmp(next5) == 0 {
            k++
            next5.Mul(five, h[k])
        }
        if h[m].Cmp(next7) == 0 {
            l++
            next7.Mul(seven, h[l])
        }
    }
    return h
}

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

func main() {
    const n = 13 * 1e6  
    h := humble(n) 
    fmt.Println("The first 50 humble numbers are:")
    fmt.Println(h[0:50])

    maxDigits := len(h[len(h)-1].String()) - 1
    counts := make([]int, maxDigits+1)
    var maxUsed int
    digits := 1
    pow10 := new(big.Int).Set(ten)
    for i := 0; i < len(h); i++ {
        for {
            if h[i].Cmp(pow10) >= 0 {
                pow10.Mul(pow10, ten)
                digits++
            } else {
                break
            }
        }  
        if digits > maxDigits {
            maxUsed = i
            break
        }
        counts[digits]++
    }
    fmt.Printf("\nOf the first %s humble numbers:\n", commatize(maxUsed))
    for i := 1; i <= maxDigits; i++ {
        s := "s"
        if i == 1 {
            s = ""
        }
        fmt.Printf("%9s have %2d digit%s\n", commatize(counts[i]), i, s)
    }       
}