Initial data commit

Task/Chowla-numbers/Visual-Basic-.NET/chowla-numbers-1.vb

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+Imports System
+
+Module Program
+    Function chowla(ByVal n As Integer) As Integer
+        chowla = 0 : Dim j As Integer, i As Integer = 2
+        While i * i <= n
+            j = n / i : If n Mod i = 0 Then chowla += i + (If(i = j, 0, j))
+            i += 1
+        End While
+    End Function
+
+    Function sieve(ByVal limit As Integer) As Boolean()
+        Dim c As Boolean() = New Boolean(limit - 1) {}, i As Integer = 3
+        While i * 3 < limit
+            If Not c(i) AndAlso (chowla(i) = 0) Then
+                Dim j As Integer = 3 * i
+                While j < limit : c(j) = True : j += 2 * i : End While
+            End If : i += 2
+        End While
+        Return c
+    End Function
+
+    Sub Main(args As String())
+        For i As Integer = 1 To 37
+            Console.WriteLine("chowla({0}) = {1}", i, chowla(i))
+        Next
+        Dim count As Integer = 1, limit As Integer = CInt((10000000.0)), power As Integer = 100,
+            c As Boolean() = sieve(limit)
+        For i As Integer = 3 To limit - 1 Step 2
+            If Not c(i) Then count += 1
+            If i = power - 1 Then
+                Console.WriteLine("Count of primes up to {0,10:n0} = {1:n0}", power, count)
+                power = power * 10
+            End If
+        Next
+        count = 0 : limit = 35000000
+        Dim p As Integer, k As Integer = 2, kk As Integer = 3
+        While True
+            p = k * kk : If p > limit Then Exit While
+            If chowla(p) = p - 1 Then
+                Console.WriteLine("{0,10:n0} is a number that is perfect", p)
+                count += 1
+            End If
+            k = kk + 1 : kk += k
+        End While
+        Console.WriteLine("There are {0} perfect numbers <= 35,000,000", count)
+        If System.Diagnostics.Debugger.IsAttached Then Console.ReadKey()
+    End Sub
+End Module

Task/Chowla-numbers/Visual-Basic-.NET/chowla-numbers-2.vb

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+Imports System.Numerics
+
+Module Program
+    Function chowla(n As Integer) As Integer
+        chowla = 0 : Dim j As Integer, i As Integer = 2
+        While i * i <= n
+            If n Mod i = 0 Then j = n / i : chowla += i : If i <> j Then chowla += j
+            i += 1
+        End While
+    End Function
+
+    Function chowla1(ByRef n As BigInteger, x As Integer) As BigInteger
+        chowla1 = 1 : Dim j As BigInteger, lim As BigInteger = BigInteger.Pow(2, x - 1)
+        For i As BigInteger = 2 To lim
+            If n Mod i = 0 Then j = n / i : chowla1 += i : If i <> j Then chowla1 += j
+        Next
+    End Function
+
+    Function sieve(ByVal limit As Integer) As Boolean()
+        Dim c As Boolean() = New Boolean(limit - 1) {}, i As Integer = 3
+        While i * 3 < limit
+            If Not c(i) AndAlso (chowla(i) = 0) Then
+                Dim j As Integer = 3 * i
+                While j < limit : c(j) = True : j += 2 * i : End While
+            End If : i += 2
+        End While
+        Return c
+    End Function
+
+    Sub Main(args As String())
+        For i As Integer = 1 To 37
+            Console.WriteLine("chowla({0}) = {1}", i, chowla(i))
+        Next
+        Dim count As Integer = 1, limit As Integer = CInt((10000000.0)), power As Integer = 100,
+            c As Boolean() = sieve(limit)
+        For i As Integer = 3 To limit - 1 Step 2
+            If Not c(i) Then count += 1
+            If i = power - 1 Then
+                Console.WriteLine("Count of primes up to {0,10:n0} = {1:n0}", power, count)
+                power = power * 10
+            End If
+        Next
+        count = 0
+        Dim p As BigInteger, k As BigInteger = 2, kk As BigInteger = 3
+        For i As Integer = 2 To 31 ' if you dare, change the 31 to 61 or 89
+            If {2, 3, 5, 7, 13, 17, 19, 31, 61, 89}.Contains(i) Then
+                p = k * kk
+                If chowla1(p, i) = p Then
+                    Console.WriteLine("{0,25:n0} is a number that is perfect", p)
+                    st = DateTime.Now
+                    count += 1
+                End If
+            End If
+            k = kk + 1 : kk += k
+        Next
+        Console.WriteLine("There are {0} perfect numbers <= {1:n0}", count, 25 * BigInteger.Pow(10, 18))
+        If System.Diagnostics.Debugger.IsAttached Then Console.ReadKey()
+    End Sub
+End Module