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

%I A023989 #16 Feb 18 2024 02:02:50
%S A023989 2,12,1112,3112,211213,312213,212223,114213,31121314,41122314,
%T A023989 31221324,21322314,21322314,21322314,21322314,21322314,21322314,
%U A023989 21322314,21322314,21322314,21322314,21322314,21322314,21322314,21322314,21322314,21322314,21322314,21322314
%N A023989 Look and Say sequence: describe the previous term! (method C - initial term is 2).
%C A023989 Method C = 'frequency' followed by 'digit'-indication with digits in increasing order.
%C A023989 Converges to 21322314 at the eleventh term.
%C A023989 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]
%C A023989 a(n) = A005151(n) for n > 6. - _Reinhard Zumkeller_, Jan 26 2014
%F A023989 a(n) = A047842(a(n-1)). - _Pontus von Brömssen_, Jun 04 2023
%e A023989 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
%o A023989 (Haskell)
%o A023989 import Data.List (group, sort, transpose)
%o A023989 a023989 n = a023989_list !! (n-1)
%o A023989 a023989_list = 2 : f [2] :: [Integer] where
%o A023989    f xs = (read $ concatMap show ys) : f (ys) where
%o A023989           ys = concat $ transpose [map length zss, map head zss]
%o A023989           zss = group $ sort xs
%o A023989 -- _Reinhard Zumkeller_, Jan 26 2014
%Y A023989 Cf. A005150, A005151, A022481.
%Y A023989 Cf. A047842, A118628.
%K A023989 nonn,base
%O A023989 0,1
%A A023989 Artemario Tadeu Medeiros da Silva (artemario(AT)uol.com.br), Mar 19 2002