<?php
$arr = array();
$n = 5;
$row = $n - 1;
$col = 0;
$row2;
$count = 1;

for (;$row >=0; $row--)
{
    $row2 = $row;
    $col = 0;
    while ($row2 <= $n - 1 && $col <= $n - 1)
    {
        $arr[$row2][$col] = $count;
        if($count == $n)
        {
            $arr[$row2][$col] = $n + 2;
        }
        elseif($count == $n+1)
        {
            $arr[$row2][$col] = $n + 1;
        }
        elseif($count == $n+2)
        {
            $arr[$row2][$col] = $n;
        }

        $row2++;
        $col++;
        $count++;

    }
}

$row = $n - 2;
$col = $n - 1;
$col2;


for (;$row >=0 ; $row--)
{
    $col2 = $col;
    $row2 = $row;

    while ($row2 >=0)
    {
        if ($count == $n*$n-2)
        {
            $arr[$row2][$col2] = $n*$n-1;
        }
        elseif ($count == $n*$n-1)
        {
            $arr[$row2][$col2] = $n*$n-2;
        }
        else
        {
            $arr[$row2][$col2] = $count;
        }
        $row2--;
        $col2--;
        $count++;
    }
}
echo "<table border='1' style='border-collapse:collapse;text-align:center;'>";
for ($i = 0; $i<$n; $i++)
{echo "<tr>";
    for($j = 0;$j<$n;$j++)
    {
        echo "<td style='width:40px;height:40px;padding:10px;'>";
        echo $arr[$i][$j];
        echo "</td>";
    }
}echo "<tr>";
echo "</table>";