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 A157261 A run-length encoding of blocks of 2 in A090822. 2
 1, 1, 1, 3, 1, 1, 1, 4, 1, 1, 1, 3, 1, 1, 1, 9, 1, 1, 1, 3, 1, 1, 1, 4, 1, 1, 1, 3, 1, 1, 1, 9, 1, 1, 1, 3, 1, 1, 1, 4, 1, 1, 1, 3, 1, 1, 1, 9, 1, 1, 1, 3, 1, 1, 1, 4, 1, 1, 1, 3, 1, 1, 1, 10, 1, 1, 1, 3, 1, 1, 1, 4, 1, 1, 1, 3, 1, 1, 1, 9, 1, 1, 1, 3, 1, 1, 1, 4, 1, 1, 1, 3, 1, 1, 1, 9, 1, 1, 1, 3, 1, 1, 1, 4, 1, 1, 1, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS The assumption underlying this sequence is that the number 2 occurs isolated or in blocks of length 3 in A090822. This sequence notes the size of successive blocks of length 3, that is, the number of blocks of length 3 not interrupted by an isolated 2. This is equivalent to counting the successive triples of indices of the form k, k+1, k+2 in A157041. Conjecture: This is not multiplicative. - N. J. A. Sloane, Jul 28 2018 LINKS Andrew Howroyd, Table of n, a(n) for n = 1..1727 EXAMPLE A090822(n)=2 at n=3 (isolated), n=6-7 (block), n=12 (isolated), n=15-17 (block), n=19 (isolated), n=22 (isolated), n=25-27 (block), n=31 (isolated) n=34-36 (block), n=38-40 (block), n=42-44 (block), n=47 (isolated). Determining the cluster size of successive blocks, we write a(1)=1 (block at n>=6), a(2)=1 (block at n>=15), a(3)=1 (block at n=>25), a(4)=3 (blocks at n>=34, n>=38, n>=42)), a(5)=1 (block at n>=53). a(16)=9 represents the 9 blocks at n>=179, n>=183, n>=187, n>=192, n>=196, n>=200,... n>=213, followed by an isolated 2 at n=223. MATHEMATICA nmax = 2000; A090822 = Cases[Import["https://oeis.org/A090822/b090822.txt", "Table"], {_, _}][[1 ;; nmax, 2]]; Length /@ DeleteCases[Split[DeleteCases[Split[A090822], s_List /; s[[1]] != 2] , #1 == #2 == {2, 2, 2}&], {{2}}] (* Jean-François Alcover, Sep 02 2019 *) CROSSREFS Cf. A090822, A157041. Sequence in context: A130605 A354872 A368335 * A079110 A079619 A318577 Adjacent sequences: A157258 A157259 A157260 * A157262 A157263 A157264 KEYWORD nonn AUTHOR Paul Curtz, Feb 26 2009 EXTENSIONS Edited by R. J. Mathar, Feb 27 2009 STATUS approved

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Last modified April 18 16:22 EDT 2024. Contains 371780 sequences. (Running on oeis4.)