On integers not of the form n - φ (n)
W. Sierpiński asked in 1959 (see , pp. 200-201, cf. ) whether there exist infinitely many positive integers not of the form n - φ(n), where φ is the Euler function. We answer this question in the affirmative by proving Theorem. None of the numbers $2^k·509203$ (k = 1, 2,...) is of the form n - φ(n).