The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A241231 Number of triangles, distinct up to congruence, on a centered hexagonal grid of size n. 5
 0, 4, 34, 134, 379, 866, 1718, 3085, 5149, 8095, 12188, 17664, 24781, 33861 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A centered hexagonal grid of size n is a grid with A003215(n-1) points forming a hexagonal lattice. LINKS Eric Weisstein's World of Mathematics, Hex Number. Eric Weisstein's World of Mathematics, Triangle. FORMULA a(n) = A241232(n) + A241233(n) + A241234(n) = A241236(n) + A241237(n). EXAMPLE For n = 2 the four kinds of non-congruent triangles are the following: /. *     * *     . *     * . . * *   . . *   * . *   . . * \. .     . .     . .     * . CROSSREFS Cf. A028419, A241223. Sequence in context: A053902 A054464 A002101 * A297715 A129557 A231518 Adjacent sequences:  A241228 A241229 A241230 * A241232 A241233 A241234 KEYWORD nonn,more AUTHOR Martin Renner, Apr 17 2014 EXTENSIONS a(7) from Martin Renner, May 31 2014 a(8)-a(14) from Giovanni Resta, May 31 2014 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 3 02:31 EST 2021. Contains 349445 sequences. (Running on oeis4.)