Template:Sequence of the Day for August 4

Intended for: August 4, 2011

Timetable

• First draft entered by Alonso del Arte on June 1, 2011 ✓
• Draft reviewed by Alonso del Arte on June 3, 2011 (same person who entered first draft due to time for review almost running out) ✓
• Draft approved by Daniel Forgues on July 4, 2011 ✓

Yesterday's SOTD * Tomorrow's SOTD

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A181832: The strong phi-torial of n (i.e. product of the positive integers

k   ≤   n

that are strongly coprime to

n

),

n   ≥   0

.

{ 1, 1, 1, 1, 1, 3, 1, 20, 15, 35, 7, 36288, 35, ... }

Back on November 5, 2010, we had A001783, the phi-torial of

n

, for Sequence of the Day. This led to the discovery of another one of those sequences that make us wonder “Why wasn’t this added to the OEIS sooner?” On pondering the phi-torial, one would think the next step would be to ask if the phi-torial of

n

is divisible by the divisorial of

n

(A007955). It’s not. However, Peter Luschny, who later on added the sequence to the OEIS, noticed that the phi-torial of

n

is divisible by the divisorial of

n  −  1

.