De Bruijn's triangle (oeis.org/A187783)

<?php

// Creating the b-file of the array https://oeis.org/A187783
// This code uses the GMP library for big integers: http://php.net/manual/en/book.gmp.php

// functions:

function pascalDiag($m, $n) {
    $return = gmp_div_q(
        gmp_fact($m * $n),
        gmp_pow(
            gmp_fact($n),
            $m
        )
    );
    return gmp_strval($return);
}

function diagCoordinates($n) {
    $arr = array();
    for ($i = 0; $i < $n; $i++) {
        for ($j = 0; $j <= $i; $j++) {
            array_push($arr, array($j, $i - $j));
        }
    }
    return $arr;
}

// create array:

$num = 55;  // For higher numbers, the entries in the b-file would have more than 1000 digits.

$arr = array();

for ($i=0; $i<=$num; $i++) {
    $row = array();
    for ($j=0; $j<=$num-$i; $j++) {
        array_push($row, pascalDiag($i,$j));
    }
    array_push($arr, $row);
}

// create b-file:

$coord = diagCoordinates($num-1);
$coordLen = count($coord);

$str = '';

for ($i=0; $i<$coordLen; $i++) {
    $val = $arr[ $coord[$i][0] ][ $coord[$i][1] ];
    $str .= $i . ' ' . $val . "\n";
}

echo $str;