<?php
$givenDayNumber = 1;             // Your value here
$date = new DateTime();          // Today (reference point)
$currentDayOfWeek = date('N');   // This is 1 = Monday, see php date manual for more options
$diff = $givenDayNumber- $currentDayOfWeek; // Difference between given number and todays number
$date->modify('+ '.$diff.' day'); // Subtract difference
$date->modify('+ 1 week');        // Add a week
echo $date->format('d/m/Y');      // Output

19/11/2012