text: eliminate indexes which does not produce primes
code: for ( let i = 1 ; i <= parseInt ( ( nNew - 1 ) / 2 ) ; i ++ ) for ( let j = ( i * ( i + 1 ) ) << 1 ; j <= parseInt ( n / 2 ) ; j = j + 2 * i + 1 ) marked [ j ] = 1 ;