A220478 Equilateral triangle from the snowflake (or E-toothpick) structure of A161330 (see Comments lines for definition).

0, 2, 4, 6, 10, 12, 16, 20, 24, 30, 34, 40, 48, 50, 54, 58, 64, 74, 80, 94, 102, 112, 126, 134, 146, 160, 164, 172, 180, 190, 206, 218, 240, 256, 272, 290, 302, 316, 332, 348, 364, 374, 386, 406, 420, 442, 464, 482, 500, 524, 542, 570, 588, 608, 636, 658, 686, 706, 724, 742

Offset: 0

Author

Omar E. Pol, Dec 22 2012

Keywords

• nonn

Comments

It appears that if n >> 1 the structure looks like an equilateral triangle, which is essentially one of the six wedges of the E-toothpick (or snowflake) structure of A161330. The sequence gives the number of E-toothpicks in the structure after n stages. A220498 (the first differences) gives the number added at the n-th round. For more information and some illustrations see A161330. For the E-toothpick right triangle see A211964.

Links

• N. J. A. Sloane, A single E-toothpick
• N. J. A. Sloane, Catalog of Toothpick and Cellular Automata Sequences in the OEIS
• Index entries for sequences related to cellular automata
• Index entries for sequences related to toothpick sequences

Crossrefs

Cf. A139250, A161328, A160120, A161330, A161336, A211964, A213360, A220498.

Formula

a(n) = n + (A161330(n) - 2)/6, n >= 1.

a(n) = n + A161336(n) = 2*A211964(n).