Abstract:
Natural numbers all of whose prime divisors (even or odd in number) belong to special sets are considered. It is proved that numbers with an odd number of different prime divisors predominate; more precisely, the difference between these numbers not exceeding a given $x$ tends to infinity with increasing $x$.
Keywords:natural number, prime divisor, Euler's identity, Dirichlet generating series, Perron's formula, Cauchy's integral theorem.