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Building block is trapezoid formed from 3 equilateral triangles; sequence gives number of pieces (polytraps) that can be formed from n such trapezoids.
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%I #18 Jul 07 2023 14:36:48

%S 1,9,94,1552,27285,509805,9783124

%N Building block is trapezoid formed from 3 equilateral triangles; sequence gives number of pieces (polytraps) that can be formed from n such trapezoids.

%C Also known as "Polytriamonds" because the building block is the unique triamond (composite of three equilateral triangles joined edge-to-edge). - _Aaron N. Siegel_, May 23 2022

%D Computed by Brendan Owen.

%H Abaroth's World, <a href="https://abarothsworld.com/Puzzles/Polyiamonds/Polyhes.htm">Polyhes, Polyhalfhexes & Polytriamonds</a>

%H Andrew Clarke, <a href="http://www.recmath.com/PolyPages/PolyPages/PolyX/PolyX.htm">Other Polyforms</a>

%Y Cf. A000577, A000228, A000105, A056844.

%K nonn,nice,hard,more

%O 1,2

%A _N. J. A. Sloane_, Oct 29 2000

%E Link updated by _William Rex Marshall_, Dec 16 2009

%E a(7) from _Aaron N. Siegel_, May 23 2022