A229461 Numbers n such that there is no convex pentagon that can be decomposed into n pairwise congruent regular equilateral triangles.

1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 13, 16, 18, 21, 22, 24, 25, 30, 33, 37, 40, 42, 45, 48, 57, 58, 70, 72, 78, 85, 88, 93, 102, 105, 120, 130, 133, 165, 168, 177, 190, 210, 232, 253, 273, 280, 312, 330, 345, 357, 385, 408, 462, 520, 760, 840, 1320, 1365, 1848

Offset

1,2

Comments

Conjecture: These 59 numbers are all such exceptions.

Terms are idoneal numbers (A000926) except for the six terms of A229462.

Numbers k not expressible as k = x^2 - y^2 - z^2 with x,y,z >= 1 and x > y+z.

Links

Table of n, a(n) for n=1..59.

Eike Hertel, Reguläre Dreieckspflasterungen konvexer Polygone, Jenaer Schriften zur Mathematik und Informatik, Math/Inf/01/13, 2013 (preprint).

Eike Hertel, Christian Richter, Tiling Convex Polygons with Congruent Equilateral Triangles, Discrete Comput Geom (2014) 51:753-759.

E. Kani, Idoneal numbers and some generalizations, Ann Sci. Math. Québec, 35 (2011), pp. 197-227.

Kival Ngaokrajang, Illustration of initial terms

Crossrefs

Cf. A000926 (idoneal numbers), A229462 (idoneal numbers not in this sequence), A229757 (hexagon exception numbers), A025052 (numbers not of form a*b+b*c+c*a).

Sequence in context: A228897 A068095 A064390 * A230709 A080671 A286608

Adjacent sequences: A229458 A229459 A229460 * A229462 A229463 A229464

Keyword

nonn

Author

Suggested by Eike Hertel, Hugo Pfoertner, Sep 24 2013

Status

approved