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A220478 Equilateral triangle from the snowflake (or E-toothpick) structure of A161330 (see Comments lines for definition). 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

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.

REFERENCES

Mohammad K. Azarian, A Trigonometric Characterization of  Equilateral Triangle, Problem 336, Mathematics and Computer Education, Vol. 31, No. 1, Winter 1997, p. 96.  Solution published in Vol. 32, No. 1, Winter 1998, pp. 84-85.

Mohammad K. Azarian, Equating Distances and Altitude in an Equilateral Triangle, Problem 316, Mathematics and Computer Education, Vol. 28, No. 3, Fall 1994, p. 337.  Solution published in Vol. 29, No. 3, Fall 1995, pp. 324-325.

LINKS

Table of n, a(n) for n=0..59.

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

FORMULA

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

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

CROSSREFS

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

Sequence in context: A005942 A024907 A033098 * A033868 A045954 A072542

Adjacent sequences:  A220475 A220476 A220477 * A220479 A220480 A220481

KEYWORD

nonn

AUTHOR

Omar E. Pol, Dec 22 2012

STATUS

approved

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Last modified November 12 14:43 EST 2019. Contains 329058 sequences. (Running on oeis4.)