随机从1-6加13

Helllo, I do randomization of elements inside the array

for ($i=0; $i<$size*$size; $i++) {
    $board[$i] = mt_rand(1, 13);
}

Now it stores random numbers from 1 to 13. What I need is to make it store numbers from 1-6 and 13. Can anyone show me the trick? Thank you for your time.

Generate a random number from 1 to 7. Then if you get 7, change it to 13.