cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A378285 Unique sequence s starting with 2,1 such that if r(r(r(s))) = s and r(s) != s and r(r(s)) != s, where r(#) denotes the runlength sequence of a sequence #.

Original entry on oeis.org

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, 1, 2, 2, 1, 2, 1, 1, 2, 2, 1, 2, 2, 1, 2, 1, 1, 2, 1, 1, 2, 2, 1, 2, 1, 1, 2, 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
Offset: 1

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Author

Clark Kimberling, Dec 20 2024

Keywords

Comments

This sequence is one of three limiting rows of the array A378282. See A378282 for a guide to related arrays and sequences.

Crossrefs

Programs

  • Mathematica
    z = 18;
    invRE[seq_, k_] := Flatten[Map[ConstantArray[#[[2]], #[[1]]] &,
        Partition[Riffle[seq, {k, 2 - Mod[k + 1, 2]}, {2, -1, 2}], 2]]];
    row1 = {1}; rows = {row1};
    col = PadRight[{}, z, {1, 1, 2}]
    Do[AppendTo[rows, invRE[Last[rows], col[[n]]]], {n, 2, Length[col]}]
    rows // ColumnForm
    Flatten[rows]   (* A378282 *)
    rows[[z - 2]];  (* A378283 *)
    rows[[z - 1]];  (* A378284 *)
    rows[[z]];      (* A378285 *)
    Map[Length, rows]   (* A378286 *)
    (* Peter J. C. Moses, Nov 21 2024 *)