Task: Abundant odd numbers
C++: #include <algorithm>
#include <iostream>
#include <numeric>
#include <sstream>
#include <vector>

std::vector<int> divisors(int n) {
    std::vector<int> divs{ 1 };
    std::vector<int> divs2;

    for (int i = 2; i*i <= n; i++) {
        if (n%i == 0) {
            int j = n / i;
            divs.push_back(i);
            if (i != j) {
                divs2.push_back(j);
            }
        }
    }
    std::copy(divs2.crbegin(), divs2.crend(), std::back_inserter(divs));

    return divs;
}

int sum(const std::vector<int>& divs) {
    return std::accumulate(divs.cbegin(), divs.cend(), 0);
}

std::string sumStr(const std::vector<int>& divs) {
    auto it = divs.cbegin();
    auto end = divs.cend();
    std::stringstream ss;

    if (it != end) {
        ss << *it;
        it = std::next(it);
    }
    while (it != end) {
        ss << " + " << *it;
        it = std::next(it);
    }

    return ss.str();
}

int abundantOdd(int searchFrom, int countFrom, int countTo, bool printOne) {
    int count = countFrom;
    int n = searchFrom;
    for (; count < countTo; n += 2) {
        auto divs = divisors(n);
        int tot = sum(divs);
        if (tot > n) {
            count++;
            if (printOne && count < countTo) {
                continue;
            }
            auto s = sumStr(divs);
            if (printOne) {
                printf("%d < %s = %d\n", n, s.c_str(), tot);
            } else {
                printf("%2d. %5d < %s = %d\n", count, n, s.c_str(), tot);
            }
        }
    }
    return n;
}

int main() {
    using namespace std;

    const int max = 25;
    cout << "The first " << max << " abundant odd numbers are:\n";
    int n = abundantOdd(1, 0, 25, false);

    cout << "\nThe one thousandth abundant odd number is:\n";
    abundantOdd(n, 25, 1000, true);

    cout << "\nThe first abundant odd number above one billion is:\n";
    abundantOdd(1e9 + 1, 0, 1, true);

    return 0;
}

Go: package main

import (
    "fmt"
    "strconv"
)

func divisors(n int) []int {
    divs := []int{1}
    divs2 := []int{}
    for i := 2; i*i <= n; i++ {
        if n%i == 0 {
            j := n / i
            divs = append(divs, i)
            if i != j {
                divs2 = append(divs2, j)
            }
        }
    }
    for i := len(divs2) - 1; i >= 0; i-- {
        divs = append(divs, divs2[i])
    }
    return divs
}

func sum(divs []int) int {
    tot := 0
    for _, div := range divs {
        tot += div
    }
    return tot
}

func sumStr(divs []int) string {
    s := ""
    for _, div := range divs {
        s += strconv.Itoa(div) + " + "
    }
    return s[0 : len(s)-3]
}

func abundantOdd(searchFrom, countFrom, countTo int, printOne bool) int {
    count := countFrom
    n := searchFrom
    for ; count < countTo; n += 2 {
        divs := divisors(n)
        if tot := sum(divs); tot > n {
            count++
            if printOne && count < countTo {
                continue
            } 
            s := sumStr(divs)
            if !printOne {
                fmt.Printf("%2d. %5d < %s = %d\n", count, n, s, tot)
            } else {
                fmt.Printf("%d < %s = %d\n", n, s, tot)
            }
        }
    }
    return n
}

func main() {
    const max = 25
    fmt.Println("The first", max, "abundant odd numbers are:")
    n := abundantOdd(1, 0, 25, false)

    fmt.Println("\nThe one thousandth abundant odd number is:")
    abundantOdd(n, 25, 1000, true)

    fmt.Println("\nThe first abundant odd number above one billion is:")
    abundantOdd(1e9+1, 0, 1, true)
}