A023989 Look and Say sequence: describe the previous term! (method C - initial term is 2).

2, 12, 1112, 3112, 211213, 312213, 212223, 114213, 31121314, 41122314, 31221324, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314, 21322314

Offset

0,1

Comments

Method C = 'frequency' followed by 'digit'-indication with digits in increasing order.

Converges to 21322314 at the eleventh term.

Depending on the initial value, the sequence may converge to a cycle of 2 or more values, for example: 123456, 111213141516, 711213141516, 61121314151617, 71121314152617, 61221314151627, 51321314152617, 51222314251617, 41421314251617, 51221334151617, 51222314251617, 41421314251617, 51221334151617. [Corrected by Pontus von Brömssen, Jun 04 2023]

a(n) = A005151(n) for n > 6. - Reinhard Zumkeller, Jan 26 2014

Links

Table of n, a(n) for n=0..28.

Formula

a(n) = A047842(a(n-1)). - Pontus von Brömssen, Jun 04 2023

Example

a(1) = 12, so a(2) = 1112 because 12 contains a digit 1 and a digit 2; a(3) = 3112 because 1112 contains three digits 1 and a digit 2

Prog

(Haskell)
import Data.List (group, sort, transpose)
a023989 n = a023989_list !! (n-1)
a023989_list = 2 : f [2] :: [Integer] where
   f xs = (read $ concatMap show ys) : f (ys) where
          ys = concat $ transpose [map length zss, map head zss]
          zss = group $ sort xs
-- Reinhard Zumkeller, Jan 26 2014

Crossrefs

Cf. A005150, A005151, A022481.

Cf. A047842, A118628.

Sequence in context: A345976 A112512 A006751 * A001389 A022914 A177361

Adjacent sequences: A023986 A023987 A023988 * A023990 A023991 A023992

Keyword

nonn,base

Author

Artemario Tadeu Medeiros da Silva (artemario(AT)uol.com.br), Mar 19 2002

Status

approved