A333030 Number of edges in an equilateral triangle "frame" of size n (see Comments in A328526 for definition).

3, 21, 132, 432, 951, 1800, 3069, 4956, 7569, 11040, 15585, 21492, 28971, 38328, 49527, 62922, 79113, 98358, 120939, 147486, 177873, 212358, 251823, 296898, 347709, 404772, 468189, 538680, 617439, 704742, 801039, 907842, 1024629, 1151544, 1289319, 1438686

Offset

1,1

Comments

For n<=3 the terms equal A274586(n). See A328526 for images of the triangular frame.

Links

Lars Blomberg, Table of n, a(n) for n = 1..65

Crossrefs

Cf. A328526 (regions), A333031 (vertices), A331776 (square frame), A274586 (filled triangle).

Sequence in context: A357783 A360626 A274586 * A125701 A124812 A141041

Adjacent sequences: A333027 A333028 A333029 * A333031 A333032 A333033

Keyword

nonn

Author

Scott R. Shannon and N. J. A. Sloane, Mar 05 2020

Extensions

a(12) and beyond from Lars Blomberg, May 01 2020

Status

approved