A190309 - OEIS

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A190309

Number of acute isosceles triangles, distinct up to congruence, on an n X n grid (or geoboard).

2

0, 0, 2, 5, 11, 19, 29, 40, 58, 74, 94, 113, 141, 168, 201, 227, 267, 304, 348, 390, 438, 483, 537, 590, 657, 709, 776, 837, 913, 979, 1057, 1130, 1225, 1299, 1396, 1472, 1576, 1663, 1768, 1863, 1974

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,3

LINKS

Table of n, a(n) for n=1..41.

Eric Weisstein's World of Mathematics, Geoboard.

Eric Weisstein's World of Mathematics, Acute Triangle.

Eric Weisstein's World of Mathematics, Isosceles Triangle.

FORMULA

a(n) = A189978(n) - A190310(n) - A108279(n).

CROSSREFS

Cf. A028419, A108279, A189978, A190021, A190310.

Sequence in context: A040147 A152471 A088796 * A161550 A245207 A215762

Adjacent sequences: A190306 A190307 A190308 * A190310 A190311 A190312

KEYWORD

nonn

AUTHOR

Martin Renner, May 08 2011

STATUS

approved