[seqfan] The "anti-Carmichael numbers" are A121707

Tomasz Ordowski tomaszordowski at gmail.com
Mon Oct 1 17:01:45 CEST 2018

Dear SeqFans!

Andrzej Schinzel and Don Reble proved my conjectures, from which it follows
that A121707 are "anti-Carmichael numbers" n defined: p-1 does not divide
n-1 for every prime p dividing n.

See https://oeis.org/A121707 (maybe someone will prove the last conjecture)
and http://www.graysage.com/djr/A121707.pdf (proof of the previous

Problem: What is the natural density D of the set of these numbers?

My conjecture: D = 2 / Pi^2.

Best regards,


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