function to calculate primes using sieve of eratosthenes
static void sieveOfEratostheneses ( ) { isPrime [ 1 ] = true ; for ( int i = 2 ; i * i < MAX ; i ++ ) { if ( ! isPrime [ i ] ) { for ( int j = 2 * i ; j < MAX ; j += i ) isPrime [ j ] = true ; } } }