function Get-SP2013ProductKey {
    $map = "BCDFGHJKMPQRTVWXY2346789"
    $value = (get-itemproperty "HKLM:\SOFTWARE\Microsoft\Office\15.0\Registration\{90150000-110D-0000-1000-0000000FF1CE}").digitalproductid
    $baseAddress = 808
    $needsN = ($value[$baseAddress + 14] -shl 3) -and 1;

    $ProductKey = ""
    for ($i = 24; $i -ge 0; $i--) {
        $r = 0
        for ($j = 13; $j -ge 0; $j--) {
            $r = ($r * 256) -bxor $value[$baseAddress + $j]
            $floor = [math]::Floor([double]($r / 24))
            $value[$baseAddress + $j] = $floor
            $r = $r % 24
        }
        $ProductKey = $map[$r] + $ProductKey
    }

    if ($needsN) {
        $firstLetterIndex = 0

        for ($i = 0; $i -lt $ProductKey.Length; $i++) {
            if ($ProductKey[0] -eq $map[$i]) {
                $firstLetterIndex = $i
                break
            }
        }

        $ProductKeyWithN = $ProductKey = $ProductKey.substring(1) # Remove first character
        $ProductKeyWithN = $ProductKeyWithN.SubString(0, $firstLetterIndex) + "N" + $ProductKeyWithN.SubString($firstLetterIndex)
        $ProductKeyWithN = $ProductKeyWithN.SubString(0, 5) + "-" + $ProductKeyWithN.SubString(5, 5) + "-" + $ProductKeyWithN.SubString(10, 5) + "-" + $ProductKeyWithN.SubString(15, 5) + "-" + $ProductKeyWithN.SubString(20, 5)
    }
    $ProductKeyWithN
}
Get-SP2013ProductKey

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