Multiplicative even functions (mod r). II Identities involving Ramanujan sums.
A sequence is called -automatic if the ’th term in the sequence can be generated by a finite state machine, reading in base as input. We show that for many multiplicative functions, the sequence is not -automatic. Among these multiplicative functions are et .
Let φ(·) and σ(·) denote the Euler function and the sum of divisors function, respectively. We give a lower bound for the number of m ≤ x for which the equation m = σ(n) - n has no solution. We also show that the set of positive integers m not of the form (p-1)/2 - φ(p-1) for some prime number p has a positive lower asymptotic density.