Write logic to print Floyd's triangle in PHP?

Floyd’s triangle is the right-angled triangle which starts with 1 and filled its rows with a consecutive number. The count of elements in next row will increment by one and the first row contains only one element.

Example of Floyd's triangle having 4 rows

The logic to print Floyd's triangle

<?php

echo "print Floyd's triangle";
echo "<pre>

 $key = 1; 
for ($i = 1; $i <= 4; $i++) { 
  for ($j = 1; $j <= $i; $j++) { 
    echo $key; 
    $key++; 
   if ($j == $i) { 
     echo "<br/>"; 
   } 
 } 
} 
echo ""; 
?>

Output:

1

2 3

4 5 6

7 8 9 10