线性筛素数

void  ( ) {
	for ( int i = 2 ; i <= n ; i ++ ) {
		if ( !v[i] ) {
			v[i] = i ;
			prim[++t] = i ;
		}
		for ( int j = 1 ; j <= t ; j ++ ) {
			if ( prim[j] > v[i] || prim[j] * i > n ) break ;
			v[prim[j]*i] = prim[j];
		}
	}
}