Conjecture on the ninth primary pseudoperfect number

A primary pseudoperfect number is a positive integer KK with the defining property that, for every prime divisor pp of KK, one has 1/K+1/p1/K+1/p equal to an integer. Let KrK_r denote a primary pseudoperfect number with rr prime factors. The known values through K8K_8 suggest the following prediction. Ninth primary pseudoperfect number conjecture. There exists exactly one primary pseudoperfect number K9K_9 with nine prime factors, and

K9(mod628)=258.K_9\pmod{6^2\cdot 8}=258.

There are no further primary pseudoperfect numbers. This is explicitly presented as a prediction motivated by the observed remainder progression; its computational verification would require searching below a 106-digit upper bound for K9K_9, and the existence of K9K_9 and the nonexistence of all later examples remain open.

Sources & referencesView supporting material

Primary source

Jonathan Sondow and Kieren MacMillan, “Primary Pseudoperfect Numbers, Arithmetic Progressions, and the Erdős-Moser Equation”, arXiv:1812.06566 (2018).

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