[seqfan] Mystery concerning sequences A169720-A169727

[Robert Munafo]

Doug,

I don't get the part where you count "3 triangles containing the
central hexagon", and "3 large triangles containing the white
hexagon". In each case I only see two triangles in the image at
oeis.org/A169720/a169720b.jpg  If you're counting a triangle twice,
why not count both of them twice?

At any rate, A169720 is much simpler than that. Note that every term
of A169720 is a term of A000217, and see my illustrations at
mrob.com/pub/math/seq-a169720.html#A169720

On 12/1/12, D. S. McNeil <dsm054 at gmail.com> wrote:
> A169720 seems to count the number of contained shapes from the inside out:
>
> 1 = 1 central hexagon
> 10 = 1 hexagon + 6 small triangles + 3 triangles containing the central
> hexagon
> 55 = 10 + 12 white triangles/hexagons + (3 tri + 1 hex) * 6 inside the
> green/blue triangles + 6 green/blue triangles + 3 large triangles
> containing the white hexagon = 22+24+9=55
> etc.

-- 
  Robert Munafo  --  mrob.com
  Follow me at: gplus.to/mrob - fb.com/mrob27 - twitter.com/mrob_27 -
mrob27.wordpress.com - youtube.com/user/mrob143 - rilybot.blogspot.com