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A166736 Consider triangles stacked so the k-th row has 2*k-1 triangles. a(n) is the number of ways to color each triangle in the first n rows using three colors with the restriction that adjacent triangles must be different colors. (Triangles are adjacent if they share a side.) 0
3, 24, 528, 31968, 5332224, 2450774016, 3104112826368 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..7.

Project Euler, Problem 189: Tri-colouring a triangular grid

EXAMPLE

Illustration of first two rows:

           /\

          /  \

         /  1 \

        /      \

       /________\

      /\        /\

     /  \      /  \

    /  2 \  3 /  4 \

   /      \  /      \

  /________\/________\

Triangles sharing a side are considered adjacent; e.g., 1 & 3 are adjacent in the figure, 1 & 2 are not.

CROSSREFS

Sequence in context: A279165 A336577 A194157 * A330297 A109055 A318766

Adjacent sequences:  A166733 A166734 A166735 * A166737 A166738 A166739

KEYWORD

nonn

AUTHOR

Chris Cole (chris(AT)questrel.com), Oct 20 2009

EXTENSIONS

Edited by Jon E. Schoenfield, Jul 08 2017

Name simplified by Charles R Greathouse IV, Jul 09 2017

STATUS

approved

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Last modified August 6 19:52 EDT 2020. Contains 336256 sequences. (Running on oeis4.)