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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 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 May 18 01:52 EDT 2022. Contains 353779 sequences. (Running on oeis4.)