I would like to make a program which can calculate first 5000 primary numbers whos ends with 9 :

I tried this but it didn't work :

$div9 = [];
$x = 2;


while (count($div9) <= 5000) {
    function findPrime($x)
    {
        for ($i = 2; $i < ($x / 2); $i  ) {
            $rest = $x % $i;
            if ($rest == 0) {
                break;
            }
        }
        return $x;
    }

    $primeList[] = $x;

    for ($j = 0; $j < count($primeList); $j  ) {
        $array = array_map('intval', str_split($primeList[$j]));
        if (end($array[$j]) === 9) {
            return $primeList[$j];
            $div9[] = $primeList[$j];
        }
    }


    $x  ;
}

any hints please?

CodePudding user response：

You should not define a function inside your while loop

This should help

function check_prime($num)
{
  if ($num == 1)
  return false;
  for ($i = 2; $i <= $num/2; $i  )
  {
    if ($num % $i == 0)
    return false;
  }
  return true;
}

$div9 = [];
$i = 0;

while(count($div9) < 5000) {
  if($i === 9 && check_prime($i)) {
    $div9[] = $i;
  }
  $i  ;
}

CodePudding user response：

Another variation on the theme, the isPrime function was ported from Javascript cryptoJS library.

# Adapted from CryptoJS v3.1.2
function isPrime( $n=0 ){
    $r=sqrt( $n );
    for( $f=2; $f <= $r; $f   ){
        if( !( $n % $f ) )return false;
    }
    return true;
}
function isFactor($n,$f){
    return $n % 10 == $f;
}

$limit=5000;
$primes=[];
$x=2;
$f=9;


while( count( $primes ) < $limit ){
    if( isPrime( $x ) && isFactor( $x, $f ) )$primes[]=$x;
    $x  ;
}


printf('<pre>%s</pre>',print_r($primes,true));