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A241224 Number of acute triangles on a centered hexagonal grid of size n. 4
0, 8, 204, 1788, 8690, 30360, 85194, 205394, 441876, 870912, 1601708, 2783574, 4616220, 7358312, 11339430, 16972182, 24763604, 35328426, 49405944, 67873484, 91762128, 122276784 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A centered hexagonal grid of size n is a grid with A003215(n-1) points forming a hexagonal lattice.

LINKS

Table of n, a(n) for n=1..22.

Eric Weisstein's World of Mathematics, Hex Number.

Eric Weisstein's World of Mathematics, Acute Triangle.

FORMULA

a(n) = A241223(n) - A241225(n) - A241226(n).

EXAMPLE

For n = 2 the eight acute triangles are the following:

/. *     * *     * .     . .     . .     . .     * .     . *

. * *   . * .   * * .   * * .   . * .   . * *   . . *   * . .

\. .     . .     . .     * .     * *     . *     * .     . *

CROSSREFS

Cf. A190019, A241223.

Sequence in context: A264124 A317631 A309904 * A259065 A204247 A063856

Adjacent sequences:  A241221 A241222 A241223 * A241225 A241226 A241227

KEYWORD

nonn

AUTHOR

Martin Renner, Apr 17 2014

EXTENSIONS

a(7) from Martin Renner, May 31 2014

a(8)-a(22) from Giovanni Resta, May 31 2014

STATUS

approved

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Last modified August 1 03:05 EDT 2021. Contains 346379 sequences. (Running on oeis4.)