duplicate hunting, pt. 18

Dean Hickerson dean at math.ucdavis.edu
Tue May 22 10:23:16 CEST 2007

Andrew Plewe wrote:

> A105143 and A105164
> http://www.research.att.com/~njas/sequences/?q=id:A105143|id:A105164

Ralf Stephan replied:

> I'm not sure. Shouldn't 10 appear in either one? Can someone run
> the Mathematica programs?

A105143 doesn't match its description or MMA program.  Since it uses the

    1->2, 2->3, 3->4, 4->5, 5->{5,4,2,1},
    6->7, 7->8, 8->9, 9->10, 10->{10,9,7,6}

and starts with a single 1, numbers larger than 5 should never occur.  Yet
the sequence contains 9, 7, 6 twice.

The second line of the mapping above is irrelevant, since those numbers
never arise.  Maybe the author intended something different for the first
half that would make the second half relevant.  Normally I'd recommend
asking him, but this particular author doesn't respond well to questions.

A105164 does match its MMA program.  10 does appear in the sequence, but
not in the first 3 lines:  a(151) = 10.

Dean Hickerson
dean at math.ucdavis.edu

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