Create a boolean array " prime [ 0 . . n ] " . A value in prime [ i ] will finally be false if i is Not a prime , else true .
bool [ ] prime = new bool [ MAX + 1 ] ; for ( int i = 0 ; i < MAX + 1 ; i ++ ) prime [ i ] = true ; for ( int p = 2 ; p * p <= MAX ; p ++ ) {