A022506 Describe previous term from the right (method A - initial term is 0).

0, 10, 1011, 211011, 21102112, 122112102112, 122112101112212211, 2122112231101112212211, 21221122311021132221221112, 12312211321321121021132221221112

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• base
• easy
• nice

Comments

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

Examples

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

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

Crossrefs

Cf. A006711, A022482, A022507-A022513.

Programs

Haskell

a022506 n = a022506_list !! n
a022506_list = 0 : 10 : iterate (a045918 . a004086) 1011
-- Reinhard Zumkeller, Mar 02 2014

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-François Alcover, Nov 26 2019 *)

Formula

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

Extensions

More terms from Erich Friedman