[seqfan] Need help with puzzling sequence A118980

Neil Sloane njasloane at gmail.com
Mon Aug 12 04:03:17 CEST 2019

Dear SeqFans, I have been cleaning up some old sequences with keyword
At the end of the weekend, this one is still a mystery: A118980.  The
puzzle boils down to this:
What is the triangle?


2, 1;

6, 5, 2;

14, 22, 18, 6;

34, 85, 118, 84, 24;

82, 311, 660, 780, 480, 120;


*All that is needed is a plausible guess for a way to continue this

The left border is said to be the "companion Pell sequence A099425", and
the right border is the factorials.

There is an explicit definition in terms of a missing sequence referred to
as "A118979" (different from the current A118979).

There are more clues involving A118981, which also need editing, (Richard
Mathar suggested a way to edit it in 2011, but I have not touched it
because I did not want to disturb the crime scene).

A118980 is a "cold case".  Richard Mathar worked on it in 2011, and I
struggled with it over the weekend.  Now I'm calling in "The Wolf" - the
combined minds of the Sequence Fans list. (The reference is to Pulp

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