A332376 Total number of edges in graph formed by the straight line segments connecting the edges of an equilateral triangle with the n-1 points resulting from a subdivision of the sides into n equal pieces.

3, 12, 39, 54, 123, 144, 255, 282, 435, 468, 663, 702, 939, 984, 1245, 1314, 1635, 1692, 2055, 2100, 2523, 2592, 3039, 3042, 3603, 3684, 4215, 4302, 4875, 4950, 5583, 5682, 6339, 6444, 7107, 7254, 7995, 8112, 8895, 8964, 9843, 9936, 10839, 10974

Offset: 1

Author

N. J. A. Sloane, Feb 13 2020

Keywords

• nonn

Links

• N. J. A. Sloane, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A091908, A092098 (number of cells), A331782 (number of vertices).

Equals three times A332377.

Formula

a(n) = A092098(n) + A331782(n) - 1 (Euler's formula).