Function to check that a number is a prime or not in O ( Math . sqrt ( N ) )
static boolean isPrime ( int N ) { if ( N < 2 ) return false ; if ( N < 4 ) return true ; if ( ( N & 1 ) == 0 ) return false ; if ( N % 3 == 0 ) return false ; int curr = 5 , s = ( int ) Math . sqrt ( N ) ;