for ($i = 0; $i < strlen($str); $i++) {
$k = 1;

for ($j = $i + 1; $j < strlen($str); $j++) {

$a_i = 0;
$b_i = $i + 1;
$p_i = $i + 1;
$m_i = $k++;
$c_i = $b_i + $m_i;
$res = false;
$formula = [];

while (1) {
$a = substr($str,$a_i,$p_i);
$b = substr($str,$b_i,$m_i);

$n = $a * $b;

$c = substr($str,$c_i,strlen($n));

//echo '<br/>' . $a . '*' . $b . '=' . $n . '->' . $c . '<br/>';

if($c){
 $formula[] = $a . '*' . $b . '=' . $n;
}

if ($c === false || $c === "") {
 break;
}

if (intval($n) == intval($c)) {
 $p_i = strlen($b);
 $m_i = strlen($n);
 $a_i = $b_i;
 $b_i = $c_i;
 $c_i = $b_i + $m_i;
 $res = true;
} else {
 $res = false;
 break;
}

}

if ($res === true) {
print_r($formula);
return true;
}

//var_dump($res) . '
';
}

}

return false;
}