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A025143 Unique sequence a of 1's and 2's such that a(1) = 2 and r(r(a)) = a != r(a), where for any sequence s, r(s) is the sequence of lengths of runs of same symbols in s; r(a) is sequence A025142. 12

%I #16 Jan 02 2024 21:09:32

%S 2,1,2,2,1,2,1,1,2,2,1,2,2,1,1,2,1,1,2,1,2,2,1,1,2,1,1,2,2,1,2,1,1,2,

%T 1,1,2,2,1,2,2,1,2,1,1,2,1,2,2,1,1,2,1,1,2,1,2,2,1,2,2,1,1,2,1,2,2,1,

%U 2,1,1,2,1,1,2,2,1,2,2,1,2,1,1,2,2,1,2,2,1,1,2,1,2,2,1,2,1,1,2,1,1,2,2,1,2,2,1,1,2,1,2

%N Unique sequence a of 1's and 2's such that a(1) = 2 and r(r(a)) = a != r(a), where for any sequence s, r(s) is the sequence of lengths of runs of same symbols in s; r(a) is sequence A025142.

%D C. Kimberling, Problem 90: Run-length sequences, Mathematische Semesterberichte, 44 (1997) 94-95.

%Y Cf. A025142.

%Y Differs from A014675 in many entries starting at entry 8.

%Y Cf. A078880 (satisfies s = r(s)), A288724 (satisfies s = r(r(r(s)))).

%K nonn

%O 1,1

%A _Clark Kimberling_

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Last modified June 23 08:04 EDT 2024. Contains 373629 sequences. (Running on oeis4.)