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 A161336 Snowflake tree sequence: (A161330(n+1) - 2)/6. 9
 0, 1, 2, 3, 6, 7, 10, 13, 16, 21, 24, 29, 36, 37, 40, 43, 48, 57, 62, 75, 82, 91, 104, 111, 122, 135, 138, 145, 152, 161, 176, 187, 208, 223, 238, 255, 266, 279, 294, 309, 324, 333, 344, 363, 376, 397, 418, 435, 452, 475, 492, 519, 536, 555, 582, 603, 630, 649, 666, 683 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS This is an E-toothpick sequence. On a triangular graph paper consider an infinite 60-degree wedge in which there is a single (and virtual) toothpick connected to its vertex. At stage 0 we start with no E-toothpicks. At stage 1 we place an E-toothpick, and so on. The sequence gives the number of E-toothpicks in the structure after n stages. A211974 (the first differences) gives the number added at the n-th stage. The structure is the tree that arise from one of the six spokes of the structure of A213360 which is essentially the same as the E-toothpick (or snowflake) structure of A161330. For n >> 1 the structure looks like a quadrilateral formed by two scalene right triangles which are joined at their hypotenuses. - Omar E. Pol, Dec 19 2012 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, A single E-toothpick N. J. A. Sloane, Catalog of Toothpick and Cellular Automata Sequences in the OEIS FORMULA a(n) = A213360(n)/6. - Omar E. Pol, Dec 20 2012 CROSSREFS Cf. A139250, A161328, A161330, A161337, A161338, A211974, A213360. Sequence in context: A069813 A266534 A293392 * A266536 A059096 A257678 Adjacent sequences:  A161333 A161334 A161335 * A161337 A161338 A161339 KEYWORD nonn AUTHOR Omar E. Pol, Jun 09 2009 EXTENSIONS Extended and edited by Omar E. Pol, Dec 19 2012 STATUS approved

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Last modified January 15 19:33 EST 2019. Contains 319171 sequences. (Running on oeis4.)