  We revisit and generalize inequalities for the summatory function of the sum
of digits in a given integer base. We prove that several known results can be
deduced from a theorem in a 2023 paper by Mohanty, Greenbury, Sarkany,
Narayanan, Dingle, Ahnert, and Louis, whose primary scope is the maximum
mutational robustness in genotype-phenotype maps.
