Emirp primes: Difference between revisions
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all emirps between 7,700 and 8,000: 7717, 7757, 7817, 7841, 7867, 7879, 7901, 7927, 7949, 7951, 7963
the 10,000th emirp: 948349</pre>
=={{header|Visual Basic .NET}}==
{{trans|C#}}
<lang vbnet>Imports System.Runtime.CompilerServices
Module Module1
<Extension()>
Function ToHashSet(Of T)(source As IEnumerable(Of T)) As HashSet(Of T)
Return New HashSet(Of T)(source)
End Function
<Extension()>
Function Reverse(number As Integer) As Integer
If number < 0 Then
Return -Reverse(-number)
End If
If number < 10 Then
Return number
End If
Dim rev = 0
While number > 0
rev = rev * 10 + number Mod 10
number = number \ 10
End While
Return rev
End Function
<Extension()>
Function Delimit(Of T)(source As IEnumerable(Of T), Optional seperator As String = " ") As String
Return String.Join(If(seperator, " "), source)
End Function
Iterator Function Primes(bound As Integer) As IEnumerable(Of Integer)
If bound < 2 Then
Return
End If
Yield 2
Dim composite As New BitArray((bound - 1) / 2)
Dim limit As Integer = Int((Int(Math.Sqrt(bound)) - 1) / 2)
For i = 0 To limit - 1
If composite(i) Then
Continue For
End If
Dim prime = 2 * i + 3
Yield prime
For j As Integer = Int((prime * prime - 2) / 2) To composite.Count - 1 Step prime
composite(j) = True
Next
Next
For i = limit To composite.Count - 1
If Not composite(i) Then
Yield 2 * i + 3
End If
Next
End Function
Iterator Function FindEmirpPrimes(limit As Integer) As IEnumerable(Of Integer)
Dim ps = Primes(limit).ToHashSet()
For Each p In ps
Dim rev = p.Reverse()
If rev <> p AndAlso ps.Contains(rev) Then
Yield p
End If
Next
End Function
Sub Main()
Dim limit = 1_000_000
Console.WriteLine("First 20:")
Console.WriteLine(FindEmirpPrimes(limit).Take(20).Delimit())
Console.WriteLine()
Console.WriteLine("Between 7700 and 8000:")
Console.WriteLine(FindEmirpPrimes(limit).SkipWhile(Function(p) p < 7700).TakeWhile(Function(p) p < 8000).Delimit())
Console.WriteLine()
Console.WriteLine("10000th:")
Console.WriteLine(FindEmirpPrimes(limit).ElementAt(9999))
End Sub
End Module</lang>
{{out}}
<pre>First 20:
13 17 31 37 71 73 79 97 107 113 149 157 167 179 199 311 337 347 359 389
Between 7700 and 8000:
7717 7757 7817 7841 7867 7879 7901 7927 7949 7951 7963
10000th:
948349</pre>
=={{header|zkl}}==
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