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On the parity of the number of multiplicative partitions and related problems. (English) Zbl 1330.11061

Summary: Let \(f(N)\) be the number of unordered factorizations of \(N\), where a factorization is a way of writing \(N\) as a product of integers all larger than 1. For example, the factorizations of 30 are \[ 2\cdot 3\cdot 5,\quad 5\cdot 6,\quad 3\cdot 10, \quad 2 \cdot 15,\quad 30, \] so that \(f(30)=5\). The function \(f(N)\), as a multiplicative analogue of the (additive) partition function \(p(N)\), was first proposed by MacMahon, and its study was pursued by Oppenheim, Szekeres and Turán, and others. Recently, A. Zaharescu and M. Zaki [Acta Arith. 145, No. 3, 221–232 (2010; Zbl 1248.11078)] showed that \(f(N)\) is even a positive proportion of the time and odd a positive proportion of the time. Here we show that for any arithmetic progression \(a\bmod m\), the set of \(N\) for which \(f(N) \equiv a\pmod m\) possesses an asymptotic density. Moreover, the density is positive as long as there is at least one such \(N\). For the case investigated by Zaharescu and Zaki (loc. cit.), we show that \(f\) is odd more than 50 percent of the time (in fact, about 57 percent).

MSC:

11N64 Other results on the distribution of values or the characterization of arithmetic functions
11B73 Bell and Stirling numbers
11P83 Partitions; congruences and congruential restrictions

Citations:

Zbl 1248.11078
Full Text: DOI

References:

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