  A set S of integers is said to be multiplicative if for every pair m and n of
coprime integers we have that mn is in S iff both m and n are in S. Both Landau
and Ramanujan gave approximations to S(x), the number of n<=x that are in S,
for specific choices of S. The asymptotical precision of their respective
approaches are being compared and related to Euler-Kronecker constants, a
generalization of Euler's constant gamma=0.57721566.... This paper claims
little originality, its aim is to give a survey on the literature related to
this theme with an emphasis on the contributions of the author (and his
coauthors).
