[seqfan] Re: Looking for sequence N1209

Joseph S. Myers jsm at polyomino.org.uk
Tue Jun 12 11:42:36 CEST 2012


On Mon, 11 Jun 2012, Neil Sloane wrote:

> Dear SeqFans,
> In the 1973 Handbook there appears this sequence, N1209:
> 1,3,15,69,309,1365,5973,25941,112065,482067,2066583,...
> It was omitted from the 1995 book, but I can't recall why.
> The definition was  WALKS ON A TRIANGULAR LATTICE, and it appeared on
> page 354 of a very long paper by Domb:

FWIW, related sequences appear under the description of "triangular strip 
polyedges" (where A151540 is one-sided triangular strip polyedges and 
A151541 is two-sided / free triangular strip polyedges, this would seem to 
be fixed triangular strip polyedges).  Ignoring the initial 1 (offset 0, I 
suppose), the initial 13 terms (fixed triangular strip polyedges with 1 to 
13 edges) are: 3, 15, 69, 309, 1365, 5973, 25941, 112065, 482067, 2066583, 
8834469, 37677603, 160367343.

-- 
Joseph S. Myers
jsm at polyomino.org.uk



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