function Get-Friday13th {
    <#
    .SYNOPSIS
        Get Friday the 13th
    .DESCRIPTION
        Get the next N Friday the 13ths
    .EXAMPLE
        Get-Friday13th
    #>
    [Alias('Friday13th', 'Friday13', 'F13')]
    param(
    # The number of Friday the 13ths to find (by default, 13)
    [ValidateRange(1,1kb)]
    [Alias('Number')]
    [int]
    $N = 13,

    # The starting date (by default, today)
    [DateTime]
    $Date = [DateTime]::Now.Date
    )

    $Day = $Date.Date

    $FridayThe13th = @()            
    do {
        # Because 5 and 13 are both prime
        # Any .DayOfWeek * .Day will be 65
        if ($day.DayOfWeek * $day.Day -eq 65) {
            $FridayThe13th += $day
        }
        $day = $day.AddDays(1)    
    } while ($FridayThe13th.Count -lt $n)
    $FridayThe13th
}

Get-Friday13th