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A036103 A look-and-say sequence: each term summarizes the previous two terms. 1

%I

%S 0,1,1110,4110,145120,1524124120,2534425120,354413624120,

%T 16355433523120,26454463424120,36456453523120,46457443522120,

%U 1736556443522120,2736556433623120,2756553463623120,2766552473622120

%N A look-and-say sequence: each term summarizes the previous two terms.

%C A look-and-say sequence. a(3) says 4 ones, 1 zero, which is the count of ones and zeros in the two previous terms. a(4) says 1 four, 5 ones, 2 zeros.

%C From the 28th term the sequence gets into a cycle of 117.

%H Reinhard Zumkeller, <a href="/A036103/b036103.txt">Table of n, a(n) for n = 0..611</a> = 5 periods

%H <a href="/index/Sa#swys">Index to sequences related to say what you see</a>

%e a(26) = 39283736554483723130;

%e a(27) = 39384726554493622120 = first term of first period;

%e a(28) = 39383736455493622120;

%e a(143) = 39283746553473823130 = last term of first period != a(26);

%e a(144) = 39384726554493622120 = first term of second period = a(27);

%e a(145) = 39383736455493622120 = a(28).

%t a[0] = 0; a[1] = 1; a[n_] := a[n] = Reverse /@ (Join[a[n-2] // IntegerDigits, a[n-1] // IntegerDigits] // Tally // SortBy[#, First]& // Reverse) // Flatten // FromDigits;

%t Array[a, 16, 0] (* _Jean-Fran├žois Alcover_, Jul 13 2016 *)

%o (Haskell)

%o import Data.List (sort, group); import Data.Function (on)

%o a036103 n = a036103_list !! n

%o a036103_list = 0 : 1 : map (read . concatMap say . group . reverse . sort)

%o (zipWith ((++) `on` show) a036103_list $ tail a036103_list)

%o where say w = (show $ length w) ++ [head w]

%o -- _Reinhard Zumkeller_, Oct 05 2015

%Y Cf. A036059.

%Y Cf. A036106.

%K base,easy,nice,nonn

%O 0,3

%A _Floor van Lamoen_

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Last modified August 12 00:34 EDT 2022. Contains 356067 sequences. (Running on oeis4.)