Factor Test

<?php

function check_factor($factor, $k, $base, $exponent, $c='-1'){

  $out  = bcpowmod($base, $exponent, $factor);
  $out  = bcmul($out, $k);
  $out  = bcadd($out, $c);
  $out  = bcmod($out, $factor);

  return $out=="0";

}

echo check_factor('28475025393798152885081', '1', '2', '3321931637')? "True!": "False!";