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A333030 Number of edges in an equilateral triangle "frame" of size n (see Comments in A328526 for definition). 5
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 (list; graph; refs; listen; history; text; internal format)
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: A125682 A125701 A274586 * A124812 A141041 A079753

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

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Last modified October 19 15:34 EDT 2021. Contains 348091 sequences. (Running on oeis4.)