Journal of Integer Sequences, Vol. 11 (2008), Article 08.1.5

Positive Integers n Such That σ(φ(n)) = σ(n)


Jean-Marie De Koninck
Départment de Mathématiques
Université Laval
Québec, PQ G1K 7P4
Canada

Florian Luca
Instituto de Matemáticas
Universidad Nacional Autónoma de México
C.P. 58089
Morelia, Michoacán
México

Abstract:

In this paper, we investigate those positive integers n for which the equality σ(φ(n)) = σ(n) holds, where σ is the sum of the divisors function and φ is the Euler function.

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(Concerned with sequences A033631 and A137733 .)

Received June 26 2007; revised version received February 9 2008. Published in Journal of Integer Sequences, February 9 2008.

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