Question

How to calculate sum of series 1 + 11 + 111 + 1111 + ... N in PHP

Answer 1

function sum_of_series($N) {
    $sum = 0;
    $tmp = 1;

    for ($i = 0; $i < $N; $i++) {
        echo $tmp . " ";
        if ($i < $N - 1) {
            echo "+ ";
        }
        $sum += $tmp;
        $tmp = ($tmp * 10) + 1;
    }
    
    return $sum;
}

$N = 6;
$sum = sum_of_series($N);

echo "= " . $sum 



/*
run:
      
1 + 11 + 111 + 1111 + 11111 + 111111 = 123456

*/

 

70+ SQL courses for beginners and professionals