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A022506 Describe previous term from the right (method A - initial term is 0). 20
0, 10, 1011, 211011, 21102112, 122112102112, 122112101112212211, 2122112231101112212211, 21221122311021132221221112, 12312211321321121021132221221112 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Method A = 'frequency' followed by 'digit'-indication.

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 0..21

Eric Weisstein's World of Mathematics, Look and Say Sequence

Wikipedia, Look-and-say sequence

FORMULA

For n > 1: a(n+1) = A045918(A004086(a(n))). - Reinhard Zumkeller, Mar 02 2014

EXAMPLE

E.g. the term after 1011 is obtained by saying "two 1's, one 0, one 1", which gives 211011.

MATHEMATICA

a[0] = 0;

a[n_] := a[n] = Split[IntegerDigits[a[n-1]]] /. L_List /; IntegerQ[L[[1]]] :> {Length[L], L[[1]]} // Reverse // Flatten // FromDigits;

a /@ Range[0, 9] (* Jean-Fran├žois Alcover, Nov 26 2019 *)

PROG

(Haskell)

a022506 n = a022506_list !! n

a022506_list = 0 : 10 : iterate (a045918 . a004086) 1011

-- Reinhard Zumkeller, Mar 02 2014

CROSSREFS

Cf. A006711, A022482, A022507-A022513.

Sequence in context: A037220 A179284 A138484 * A127117 A154703 A172163

Adjacent sequences:  A022503 A022504 A022505 * A022507 A022508 A022509

KEYWORD

nonn,base,easy,nice

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from Erich Friedman.

STATUS

approved

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Last modified January 26 05:10 EST 2020. Contains 331273 sequences. (Running on oeis4.)