A333032 Number of triangular regions in an equilateral triangular "frame" of size n (see Comments in A328526 for definition).

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

Author

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

Keywords

• nonn

Comments

See A328526 for images of the triangular frame.

Links

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

Crossrefs

Cf. A328526 (regions), A333030 (edges), A333031 (vertices), A333033 (4-gons), A331776 (square frame), A274586 (filled triangle).

Extensions

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