cp's OEIS Frontend

A006711 Describe previous term from the right (method A - initial term is 1).

%I A006711 M4778 #25 Feb 16 2025 08:32:30
%S A006711 1,11,21,1112,1231,11131211,2112111331,112331122112,12212221231221,
%T A006711 11221113121132112211,212221121321121113312221,
%U A006711 113211233112211213111221321112
%N A006711 Describe previous term from the right (method A - initial term is 1).
%C A006711 Method A = 'frequency' followed by 'digit'-indication.
%D A006711 J. H. Conway, personal communication.
%D A006711 Akhlesh Lakhtakia and C. A. Pickover, Observations on the Gleichniszahlen-Reihe: An Unusual Number Theory Sequence, J. Rec. Math., Vol. 25 #3, pp. 189-192, 1993.
%D A006711 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A006711 Reinhard Zumkeller, <a href="/A006711/b006711.txt">Table of n, a(n) for n = 1..24</a>
%H A006711 Onno M. Cain, Sela T. Enin, <a href="https://arxiv.org/abs/2004.00209">Inventory Loops (i.e. Counting Sequences) have Pre-period 2 max S_1 + 60</a>, arXiv:2004.00209 [math.NT], 2020.
%H A006711 Trevor Scheopner, <a href="http://pumj.org/docs/Issue1/Article_4.pdf">The Cyclic Nature (and Other Intriguing Properties) of Descriptive Numbers</a>, Princeton Undergraduate Mathematics Journal, Issue 1, Article 4.
%H A006711 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LookandSaySequence.html">Look and Say Sequence</a>
%H A006711 Wikipedia, <a href="http://en.wikipedia.org/wiki/Look-and-say_sequence">Look-and-say sequence</a>
%F A006711 a(n+1) = A045918(A004086(a(n))). - _Reinhard Zumkeller_, Mar 02 2014
%e A006711 E.g. the term after 1231 is obtained by saying "one 1, one 3, one 2, one 1", which gives 11131211.
%t A006711 A006711[1]:=1;A006711[n_]:=A006711[n]=FromDigits[Flatten[{Length[#],First[#]}&/@Split[Reverse[IntegerDigits[A006711[n-1]]]]]];Map[A006711,Range[15]] (* _Peter J. C. Moses_, Apr 22 2013 *)
%o A006711 (Haskell)
%o A006711 a006711 n = a006711_list !! (n-1)
%o A006711 a006711_list = iterate (a045918 . a004086) 1
%o A006711 -- _Reinhard Zumkeller_, Mar 02 2014
%Y A006711 Cf. A005150, A022506, A022482, A022507-A022513.
%K A006711 nonn,base,easy,nice
%O A006711 1,2
%A A006711 _N. J. A. Sloane_