Create a boolean array " prime [ 0 . . n ] " and initialize all entries it as true . A value in prime [ i ] will finally be false if i is Not a prime , else true .
prime = [ None ] * ( n + 1 ) NEW_LINE for i in range ( len ( prime ) ) : NEW_LINE INDENT prime [ i ] = True NEW_LINE DEDENT p = 2 NEW_LINE while p * p <= n : NEW_LINE