The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A241239 Number of obtuse isosceles triangles, distinct up to congruence, on a centered hexagonal grid of size n. 1
 0, 1, 4, 10, 19, 30, 45, 61, 84, 106, 134, 165, 199, 234, 277, 321, 364, 412, 478, 523, 595 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 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, Obtuse Triangle. Eric Weisstein's World of Mathematics, Isosceles Triangle. FORMULA a(n) = A241237(n) - A241238(n). EXAMPLE For n = 2 the only kind of non-congruent obtuse isosceles triangles is the following: /* * . . * \. . CROSSREFS Cf. A190310, A241230. Sequence in context: A267882 A238705 A022785 * A057312 A219965 A008038 Adjacent sequences: A241236 A241237 A241238 * A241240 A241241 A241242 KEYWORD nonn,more AUTHOR Martin Renner, Apr 17 2014 EXTENSIONS a(7) from Martin Renner, May 31 2014 a(8)-a(21) 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified February 2 03:35 EST 2023. Contains 359997 sequences. (Running on oeis4.)