

A341688


The number of regions inside a 2 by 1 ellipse formed by the straight line segments mutually connecting all points formed by dividing the ellipse into 2n equal angle sectors from its origin.


4



0, 4, 24, 84, 232, 524, 1052, 1868, 3144, 4876, 7440, 10724, 15124, 20604, 27632, 36124, 46672, 59108, 74184, 91488, 112380, 136044, 163724, 194924, 230932, 271124, 316992, 367748, 425124, 488116, 558820, 635964, 721824, 815044, 918132, 1029524, 1152012, 1283788, 1427964, 1582328, 1750760
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OFFSET

1,2


COMMENTS

The ellipse, with width twice its height, has points at its xaxis extrema and n1 points both above and below the xaxis, 2n points in total. These are placed on the ellipse's perimeter by dividing it from the origin into 2n sectors of equal angle.
The terms are from numeric computation  no formula for a(n) is currently known.


LINKS

Table of n, a(n) for n=1..41.
Scott R. Shannon, Regions for n = 3.
Scott R. Shannon, Regions for n = 5.
Scott R. Shannon, Regions for n = 9.
Scott R. Shannon, Regions for n = 19.
Scott R. Shannon, Regions for n = 24.
Scott R. Shannon, Regions for n = 13 using random distancebased coloring.
Wikipedia, Ellipse.


CROSSREFS

Cf. A341762 (vertices), A341764 (edges), A341800 (ngons), A007678, A092867, A255011, A331929, A331931, A333075.
Sequence in context: A212135 A210569 A334581 * A341877 A005561 A061612
Adjacent sequences: A341685 A341686 A341687 * A341689 A341690 A341691


KEYWORD

nonn


AUTHOR

Scott R. Shannon and N. J. A. Sloane, Feb 17 2021


STATUS

approved



