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A006928
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a(n) = length of (n+1)st run, with initial terms 1, 2.
(Formerly M0070)
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14
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1, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1, 2, 1, 1, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 1, 1, 2, 1, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 1, 2, 2, 1, 2, 1, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1, 2, 1, 1, 2, 1, 2, 2, 1
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OFFSET
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1,2
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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Table of n, a(n) for n=1..108.
Eric Weisstein's World of Mathematics, Kolakoski Sequence.
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FORMULA
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Essentially same as Kolakoski sequence A000002.
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EXAMPLE
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Start with [ 1,2 ]. a(1)=1, so the second run has length 1, so a(3) must be 1. a(2)=2, so the third run has length 2, so a(4) must also be 1 and a(5) must be 2. a(3)=1, so the 4th run has length 1, so a(6) must be 1; etc. (From Labos E.)
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PROG
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(PARI) a=[ 1, 2 ]; for(n=2, 80, for(i=1, a[ n ], a=concat(a, 1+(n%2)))); a
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CROSSREFS
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A006928(n)=A000002(n+1), n>1.
Sequence in context: A090629 A086412 A192006 * A087890 A008676 A025893
Adjacent sequences: A006925 A006926 A006927 * A006929 A006930 A006931
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KEYWORD
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nonn,easy,nice
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AUTHOR
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N. J. A. Sloane.
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STATUS
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approved
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