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