I noticed that the earlier way to find primes is really fast for small numbers, but it is really really slow for number >5000

To shorten this, and provide a proper track of what primes are found as well as looping endlessly I’ve created this thing below.

Place it as prime.ps1 in a folder with read/write access.

The code below writes lines in a file called primes.log and keeps a progress of the last processed number (stored in progress.log).

This allows the script to resume the last location where it was terminated.

It also uses a better algorithm to determine if the given number is a prime or not, resulting in a steady 30 seconds to calculate 0-5000

Now the algorithm is not perfect (could check common divisible numbers first and some pattern matching) but it produces a steady stream of numbers in a fairly quick fashion.

[CmdletBinding()] Param() Process{ If(!([int]$currentNumber = Get-Content $progressfile -ErrorAction Ignore)){[int]$currentNumber = $lastPrime+1} Write-Verbose "Starting at $currentNumber" "$(Get-Date -UFormat "%Y-%m-%d %r")| Starting at $currentNumber" | Out-File $logfile -Append While($Loop){ Write-Verbose "Processing $currentNumber" $prime = Test-Prime $currentNumber If($prime){ $currentNumber | Out-File $file -Append "$(Get-Date -UFormat "%Y-%m-%d %r")| Found prime, $currentNumber" | Out-File $logfile -Append Write-host "Success, prime found! $currentNumber" -ForegroundColor Green } $currentNumber++ $currentNumber | Out-File $progressfile } } Begin{ $MyPath = Split-Path $MyInvocation.MyCommand.path -Parent $Loop = $true $logfile = "$MyPath\log.log" $file = "$MyPath\primes.log" $progressfile = "$MyPath\progress.log" Try{ $primes = Get-Content $file -ErrorAction Ignore [int]$lastPrime = $primes[-1] Write-Verbose "File found, last prime is $lastprime" } Catch{ Write-Verbose "File not found. Creating file and starting from 3" $lastPrime = 3 New-Item -Path $file -ItemType file -Force "2","3" | ForEach-Object{$_ | Out-File $file -Append} } Function Test-Prime{ Param($number) If($number -match "0$|2$|4$|5$|6$|8$"){ return $false } [int]$DivNumber = $number/2 #$numbers = 2..$DivNumber $i = 2 While($i -le $DivNumber){ If($number%$i -eq 0){ return $false } $i++ } return $true } }