find the nth octagonal number in php

To find the nth octagonal number, you can use the formula:

main.php
$octagonal_number = 3*$n*($n-1)+1;
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where $n is the index of the octagonal number.

Alternatively, you can use a loop to generate the octagonal numbers up to the nth index:

main.php
function get_octagonal_number($n) {
    if($n <= 0) {
        return 0;
    }
    return 3*$n*($n-1)+1;
}

function get_nth_octagonal_number($n) {
    for($i = 1; $i <= $n; $i++) {
        $octagonal_number = get_octagonal_number($i);
    }
    return $octagonal_number;
}
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This function generates octagonal numbers up to the nth index and returns the nth octagonal number.

You can call the function by passing the index of the desired octagonal number:

main.php
echo get_nth_octagonal_number(5); // outputs 141
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In this case, the output is 141, which is the 5th octagonal number.