[PHPID QUIZ] Deret Bilangan

DeretBilangan.php

<?php

class DeretBilangan
{
    private function isPrima($number)
    {
        $flag = 0;
        for ($i = 1; $i <= $number; $i++) {
            if (0 === $number % $i) {
                $flag++;
            }
        }

        if (2 === $flag) {
            return true;
        }

        return false;
    }

    private function isGenap($number)
    {
        if (0 === $number % 2) {
            return true;
        }

        return false;
    }

    public function count($limit)
    {
        $ganjil = array();
        $genap = array();
        $prima = array();
        $numbers = array();
        for ($i=1; $i <= $limit; $i++) {
            $angka = ($i + 1) * ($i - 1);
            
            $numbers[] = $angka;

            if ($this->isGenap($angka)) {
                $genap[] = $angka;
            } else {
                $ganjil[] = $angka;
            }

            if ($this->isPrima($angka)) {
                $prima[] = $angka;
            }
        }
        
        echo sprintf('Deret (%d): %s', count($numbers), implode(', ', $numbers));
        echo PHP_EOL; 
        echo sprintf('Ganjil (%d): %s', count($ganjil), implode(', ', $ganjil));
        echo PHP_EOL; 
        echo sprintf('Genap (%d): %s', count($genap), implode(', ', $genap));
        echo PHP_EOL; 
        echo sprintf('Prima (%d): %s', count($prima), implode(', ', $prima));
        echo PHP_EOL;        
    }
}

$deret = new DeretBilangan();
$deret->count(100);