$files = (Get-ChildItem ./* -Include *.mp4).BaseName
# Write-Host $files
$numbers = @()
foreach ($file in $files) {
    $numbers += [int]($file)
}
# Write-Host $numbers
if ($numbers.Length -ne $files.Length) {
    for($i = 0; $i -lt $numbers.Length; $i++) {
        if (($numbers[$i]+1) -ne $numbers[$i+1]) {
            Write-Host $numbers[$i]
        }
    }
} else {
    Write-Host "No gaps found"
}