“…The recent years, a lot of progress has been made on our understanding of digits of multiplicatively constrained integers (e.g. primes): see [20,19,11,44,45,28,14] for sum of digits of primes in residue classes, [29,7,65] for primes with restricted digits, or [43,15,17,46,16] for digits of polynomials. Here we are interested in two particular digital functions (defined in terms of digit expansion), the sum-of-digits function…”