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.

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, 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, 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

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

References

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

Crossrefs

Cf. A025142.

Differs from A014675 in many entries starting at entry 8.

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