A161830 Y-toothpick triangle (see Comments lines for definition).

0, 1, 3, 5, 9, 11, 15, 19, 27, 31, 35, 39, 47, 53, 61, 71, 89, 99, 103

Offset: 0

Author

Omar E. Pol, Jun 20 2009

Keywords

• more
• nonn

Comments

Y-toothpick sequence starting at the corner of an infinite hexagon in which its vertex touch an endpoint of the initial Y-toothpick and the two other endpoints are equidistant from the nearest sides of the hexagon.

The sequence gives the number of Y-toothpicks in the structure after n rounds. A161831 (the first differences) gives the number added at the n-th round.

See the Y-toothpick sequence A160120 for more information about the recursive, fractal-like structure.

Links

• David Applegate, Omar E. Pol and N. J. A. Sloane, The Toothpick Sequence and Other Sequences from Cellular Automata, Congressus Numerantium, Vol. 206 (2010), 157-191. [There is a typo in Theorem 6: (13) should read u(n) = 4.3^(wt(n-1)-1) for n >= 2.]
• N. J. A. Sloane, Catalog of Toothpick and Cellular Automata Sequences in the OEIS

Crossrefs

Cf. A139250, A160120, A160121, A160406, A160407, A161831, A161832, A161833.