Task: Weird numbers
C: #include "stdio.h"
#include "stdlib.h"
#include "stdbool.h"
#include "string.h"

struct int_a {
    int *ptr;
    size_t size;
};

struct int_a divisors(int n) {
    int *divs, *divs2, *out;
    int i, j, c1 = 0, c2 = 0;
    struct int_a array;

    divs = malloc(n * sizeof(int) / 2);
    divs2 = malloc(n * sizeof(int) / 2);
    divs[c1++] = 1;

    for (i = 2; i * i <= n; i++) {
        if (n % i == 0) {
            j = n / i;
            divs[c1++] = i;
            if (i != j) {
                divs2[c2++] = j;
            }
        }
    }

    out = malloc((c1 + c2) * sizeof(int));
    for (int i = 0; i < c2; i++) {
        out[i] = divs2[i];
    }
    for (int i = 0; i < c1; i++) {
        out[c2 + i] = divs[c1 - i - 1];
    }
    array.ptr = out;
    array.size = c1 + c2;

    free(divs);
    free(divs2);
    return array;
}

bool abundant(int n, struct int_a divs) {
    int sum = 0;
    int i;
    for (i = 0; i < divs.size; i++) {
        sum += divs.ptr[i];
    }
    return sum > n;
}

bool semiperfect(int n, struct int_a divs) {
    if (divs.size > 0) {
        int h = *divs.ptr;
        int *t = divs.ptr + 1;

        struct int_a ta;
        ta.ptr = t;
        ta.size = divs.size - 1;

        if (n < h) {
            return semiperfect(n, ta);
        } else {
            return n == h
                || semiperfect(n - h, ta)
                || semiperfect(n, ta);
        }
    } else {
        return false;
    }
}

bool *sieve(int limit) {
    bool *w = calloc(limit, sizeof(bool));
    struct int_a divs;
    int i, j;

    for (i = 2; i < limit; i += 2) {
        if (w[i]) continue;
        divs = divisors(i);
        if (!abundant(i, divs)) {
            w[i] = true;
        } else if (semiperfect(i, divs)) {
            for (j = i; j < limit; j += i) {
                w[j] = true;
            }
        }
    }

    free(divs.ptr);
    return w;
}

int main() {
    bool *w = sieve(17000);
    int count = 0;
    int max = 25;
    int n;

    printf("The first 25 weird numbers:\n");
    for (n = 2; count < max; n += 2) {
        if (!w[n]) {
            printf("%d ", n);
            count++;
        }
    }
    printf("\n");

    free(w);
    return 0;
}

VB: Module Module1

    Dim resu As New List(Of Integer)

    Function TestAbundant(n As Integer, ByRef divs As List(Of Integer)) As Boolean
        divs = New List(Of Integer)
        Dim sum As Integer = -n : For i As Integer = Math.Sqrt(n) To 1 Step -1
            If n Mod i = 0 Then divs.Add(i) : Dim j As Integer = n / i : divs.Insert(0, j) : sum += i + j
        Next : divs(0) = sum - divs(0) : Return divs(0) > 0
    End Function

    Function subList(src As List(Of Integer), Optional first As Integer = Integer.MinValue) As List(Of Integer)
        subList = src.ToList : subList.RemoveAt(1)
    End Function

    Function semiperfect(divs As List(Of Integer)) As Boolean
        If divs.Count < 2 Then Return False
        Select Case divs.First.CompareTo(divs(1))
            Case 0 : Return True
            Case -1 : Return semiperfect(subList(divs))
            Case 1 : Dim t As List(Of Integer) = subList(divs) : t(0) -= divs(1)
                If semiperfect(t) Then Return True Else t(0) = divs.First : Return semiperfect(t)
        End Select : Return False 
    End Function

    Function Since(et As TimeSpan) As String 
        If et > New TimeSpan(2000000) Then
            Dim s As String = " " & et.ToString(), p As Integer = s.IndexOf(":"), q As Integer = s.IndexOf(".")
            If q < p Then s = s.Insert(q, "Days") : s = s.Replace("Days.", "Days, ")
            p = s.IndexOf(":") : s = s.Insert(p, "h") : s = s.Replace("h:", "h ")
            p = s.IndexOf(":") : s = s.Insert(p, "m") : s = s.Replace("m:", "m ")
            s = s.Replace(" 0", " ").Replace(" 0h", " ").Replace(" 0m", " ") & "s"
            Return s.TrimStart()
        Else
            If et > New TimeSpan(1500) Then
                Return et.TotalMilliseconds.ToString() & "ms"
            Else
                If et > New TimeSpan(15) Then
                    Return (et.TotalMilliseconds * 1000.0).ToString() & "µs"
                Else
                    Return (et.TotalMilliseconds * 1000000.0).ToString() & "ns"
                End If
            End If
        End If
    End Function

    Sub Main(args As String())
        Dim sw As New Stopwatch, st As Integer = 2, stp As Integer = 1020, count As Integer = 0
        Dim max As Integer = 25, halted As Boolean = False
        If args.Length > 0 Then _
            Dim t As Integer = Integer.MaxValue : If Integer.TryParse(args(0), t) Then max = If(t > 0, t, Integer.MaxValue)
        If max = Integer.MaxValue Then
            Console.WriteLine("Calculating weird numbers, press a key to halt.")
            stp *= 10
        Else
            Console.WriteLine("The first {0} weird numbers:", max)
        End If
        If max < 25 Then stp = 140
        sw.Start()
        Do : Parallel.ForEach(Enumerable.Range(st, stp),
            Sub(n)
                Dim divs As List(Of Integer) = Nothing
                If TestAbundant(n, divs) AndAlso Not semiperfect(divs) Then
                    SyncLock resu : resu.Add(n) : End SyncLock
                End If
            End Sub)
            If resu.Count > 0 Then
                resu.Sort()
                If count + resu.Count > max Then
                    resu = resu.Take(max - count).ToList
                End If
                Console.Write(String.Join(" ", resu) & " ")
                count += resu.Count : resu.Clear()
            End If
            If Console.KeyAvailable Then Console.ReadKey() : halted = True : Exit Do
            st += stp
        Loop Until count >= max
        sw.Stop()
        If max < Integer.MaxValue Then
            Console.WriteLine(vbLf & "Computation time was {0}.", Since(sw.Elapsed))
            If halted Then Console.WriteLine("Halted at number {0}.", count)
        Else
            Console.WriteLine(vbLf & "Computation time was {0} for the first {1} weird numbers.", Since(sw.Elapsed), count)
        End If
    End Sub
End Module