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A270641 The sequence a of 1's and 2's starting with (1,1,1,1) such that a(n) is the length of the (n+1)st run of a. 8
1, 1, 1, 1, 2, 1, 2, 1, 2, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1, 2, 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, 1, 2, 1, 1, 2, 2, 1, 2, 1, 1, 2, 1, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

Guide to related sequences (with adjustments for initial terms):

1, 1, 1, 1;    a(n) = length of (n + 1)st run of a; A270641

1, 1, 1, 2;    a(n) = length of (n + 2)nd run of a; A270641

1, 1, 2, 1;    a(n) = length of (n + 3)rd run of a; A270641

1, 1, 2, 2;    a(n) = length of (n + 2)nd run of a; A270642

1, 2, 1, 1;    a(n) = length of (n + 3)rd run of a; A022300

1, 2, 1, 2;    a(n) = length of (n + 4)th run of a; A270641

1, 2, 2, 1;    a(n) = length of (n + 3)rd run of a; A270643

1, 2, 2, 2;    a(n) = length of (n + 2)nd run of a; A270644

2, 1, 1, 1;    a(n) = length of (n + 2)nd run of a; A270645

2, 1, 1, 2;    a(n) = length of (n + 3)rd run of a; A222300

2, 1, 2, 1;    a(n) = length of (n + 4)th run of a; A270641

2, 1, 2, 2;    a(n) = length of (n + 3)rd run of a; A000002 (Kolakoski)

2, 2, 1, 1;    a(n) = length of (n + 2)nd run of a; A270646

2, 2, 1, 2;    a(n) = length of (n + 3)rd run of a; A270647

2, 2, 2, 1;    a(n) = length of (n + 2)nd run of a; A270644

2, 2, 2, 2;    a(n) = length of (n + 1)st run of a; A270648

LINKS

Clark Kimberling, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1) = 1, so the 2nd run has length 1, so a(5) must be 2 and a(6) = 1.

a(2) = 1, so the 3rd run has length 1, so a(7) = 2.

a(3) = 1, so the 4th run has length 1, so a(8) = 1.

a(4) = 1, so the 5th run has length 1, so a(9) = 2.

a(5) = 2, so the 6th run has length 2, so a(10) = 2 and a(11) = 1.

Globally, the runlength sequence of a is 4,1,1,1,1,2,1,2,1,2,2,1,...., and deleting the first term leaves a = A270641.

MATHEMATICA

a = {1, 1, 1, 1};

Do[a = Join[a, ConstantArray[If[Last[a] == 1, 2, 1], {a[[n]]}]], {n,   200}]; a

(* Peter J. C. Moses, Apr 01 2016 *)

CROSSREFS

Cf. A000002, A006928, A022300,

Sequence in context: A080573 A186440 A006340 * A076371 A175044 A106149

Adjacent sequences:  A270638 A270639 A270640 * A270642 A270643 A270644

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, Apr 05 2016

STATUS

approved

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Last modified May 10 15:15 EDT 2021. Contains 343773 sequences. (Running on oeis4.)