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A333032
Number of triangular regions in an equilateral triangular "frame" of size n (see Comments in A328526 for definition),
4
1, 12, 48, 147, 291, 519, 879, 1383, 2079, 3039, 4359, 5991, 7983, 10515, 13731, 17571, 22131, 27543, 33951, 41271, 49599, 59355, 70779, 83499, 97611, 113763, 132243, 152619, 175035, 199707, 226827, 256443, 288747, 324603, 364395, 407139, 452979, 503319
OFFSET
1,2
COMMENTS
See A328526 for images of the triangular frame.
LINKS
CROSSREFS
Cf. A328526 (regions), A333030 (edges), A333031 (vertices), A333033 (4-gons), A331776 (square frame), A274586 (filled triangle).
Sequence in context: A292022 A265040 A059162 * A190622 A117027 A161171
KEYWORD
nonn
AUTHOR
EXTENSIONS
a(12) and beyond from Lars Blomberg, May 01 2020
STATUS
approved