Task: Aliquot sequence classifications


C++: #include <cstdint>
#include <iostream>
#include <string>

using integer = uint64_t;


integer divisor_sum(integer n) {
    integer total = 1, power = 2;
    
    for (; n % 2 == 0; power *= 2, n /= 2)
        total += power;
    
    for (integer p = 3; p * p <= n; p += 2) {
        integer sum = 1;
        for (power = p; n % p == 0; power *= p, n /= p)
            sum += power;
        total *= sum;
    }
    
    if (n > 1)
        total *= n + 1;
    return total;
}


void classify_aliquot_sequence(integer n) {
    constexpr int limit = 16;
    integer terms[limit];
    terms[0] = n;
    std::string classification("non-terminating");
    int length = 1;
    for (int i = 1; i < limit; ++i) {
        ++length;
        terms[i] = divisor_sum(terms[i - 1]) - terms[i - 1];
        if (terms[i] == n) {
            classification =
                (i == 1 ? "perfect" : (i == 2 ? "amicable" : "sociable"));
            break;
        }
        int j = 1;
        for (; j < i; ++j) {
            if (terms[i] == terms[i - j])
                break;
        }
        if (j < i) {
            classification = (j == 1 ? "aspiring" : "cyclic");
            break;
        }
        if (terms[i] == 0) {
            classification = "terminating";
            break;
        }
    }
    std::cout << n << ": " << classification << ", sequence: " << terms[0];
    for (int i = 1; i < length && terms[i] != terms[i - 1]; ++i)
        std::cout << ' ' << terms[i];
    std::cout << '\n';
}

int main() {
    for (integer i = 1; i <= 10; ++i)
        classify_aliquot_sequence(i);
    for (integer i : {11, 12, 28, 496, 220, 1184, 12496, 1264460, 790, 909, 562,
                      1064, 1488})
        classify_aliquot_sequence(i);
    classify_aliquot_sequence(15355717786080);
    classify_aliquot_sequence(153557177860800);
    return 0;
}



Go: package main

import (
    "fmt"
    "math"
    "strings"
)

const threshold = uint64(1) << 47

func indexOf(s []uint64, search uint64) int {
    for i, e := range s {
        if e == search {
            return i
        }
    }
    return -1
}

func contains(s []uint64, search uint64) bool {
    return indexOf(s, search) > -1
}

func maxOf(i1, i2 int) int {
    if i1 > i2 {
        return i1
    }
    return i2
}

func sumProperDivisors(n uint64) uint64 {
    if n < 2 {
        return 0
    }
    sqrt := uint64(math.Sqrt(float64(n)))
    sum := uint64(1)
    for i := uint64(2); i <= sqrt; i++ {
        if n % i != 0 {
            continue
        }
        sum += i + n / i
    }
    if sqrt * sqrt == n {
        sum -= sqrt
    }
    return sum
}

func classifySequence(k uint64) ([]uint64, string) {
    if k == 0 {
        panic("Argument must be positive.")
    }
    last := k
    var seq []uint64
    seq = append(seq, k)
    for {
        last = sumProperDivisors(last)
        seq = append(seq, last)
        n := len(seq)
        aliquot := ""
        switch {
        case last == 0:
            aliquot = "Terminating"
        case n == 2 && last == k:
            aliquot = "Perfect"
        case n == 3 && last == k:
            aliquot = "Amicable"
        case n >= 4 && last == k:
            aliquot = fmt.Sprintf("Sociable[%d]", n - 1)
        case last == seq[n - 2]:
            aliquot = "Aspiring"
        case contains(seq[1 : maxOf(1, n - 2)], last):
            aliquot = fmt.Sprintf("Cyclic[%d]", n - 1 - indexOf(seq[:], last))
        case n == 16 || last > threshold:
            aliquot = "Non-Terminating"
        }
        if aliquot != "" {
            return seq, aliquot
        }
    }
}

func joinWithCommas(seq []uint64) string {
    res := fmt.Sprint(seq)
    res = strings.Replace(res, " ", ", ", -1)
    return res
}

func main() {
    fmt.Println("Aliquot classifications - periods for Sociable/Cyclic in square brackets:\n")
    for k := uint64(1); k <= 10; k++ {
        seq, aliquot := classifySequence(k)
        fmt.Printf("%2d: %-15s %s\n", k, aliquot, joinWithCommas(seq))
    }
    fmt.Println()

    s := []uint64{
        11, 12, 28, 496, 220, 1184, 12496, 1264460, 790, 909, 562, 1064, 1488,
    }
    for _, k := range s {
        seq, aliquot := classifySequence(k)
        fmt.Printf("%7d: %-15s %s\n",  k, aliquot, joinWithCommas(seq))
    }
    fmt.Println()

    k := uint64(15355717786080)
    seq, aliquot := classifySequence(k)
    fmt.Printf("%d: %-15s %s\n", k, aliquot, joinWithCommas(seq))
}