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A001145 Describe the previous term! (method A - initial term is 7).

%I A001145 #24 Apr 14 2019 10:26:30
%S A001145 7,17,1117,3117,132117,1113122117,311311222117,13211321322117,
%T A001145 1113122113121113222117,31131122211311123113322117,
%U A001145 132113213221133112132123222117
%N A001145 Describe the previous term! (method A - initial term is 7).
%C A001145 Method A = 'frequency' followed by 'digit'-indication.
%C A001145 a(n+1) - a(n) is divisible by 10^5 for n > 5. - _Altug Alkan_, Dec 04 2015
%D A001145 S. R. Finch, Mathematical Constants, Cambridge, 2003, pp. 452-455.
%D A001145 I. Vardi, Computational Recreations in Mathematica. Addison-Wesley, Redwood City, CA, 1991, p. 4.
%H A001145 T. D. Noe, <a href="/A001145/b001145.txt">Table of n, a(n) for n=1..20</a>
%H A001145 J. H. Conway, <a href="http://dx.doi.org/10.1007/978-1-4612-4808-8_53">The weird and wonderful chemistry of audioactive decay</a>, in T. M. Cover and Gopinath, eds., Open Problems in Communication and Computation, Springer, NY 1987, pp. 173-188.
%H A001145 S. R. Finch, <a href="http://www.people.fas.harvard.edu/~sfinch/constant/cnwy/cnwy.html">Conway's Constant</a> [Broken link]
%H A001145 S. R. Finch, <a href="http://web.archive.org/web/20010207194413 /http://www.mathsoft.com/asolve/constant/cnwy/cnwy.html">Conway's Constant</a> [From the Wayback Machine]
%e A001145 E.g. the term after 3117 is obtained by saying "one 3, two 1's, one 7", which gives 132117.
%t A001145 RunLengthEncode[x_List] := (Through[{First, Length}[ #1]] &) /@ Split[x]; LookAndSay[n_, d_: 1] := NestList[Flatten[Reverse /@ RunLengthEncode[ # ]] &, {d}, n - 1]; F[n_] := LookAndSay[n, 7][[n]]; Table[FromDigits[F[n]], {n, 1, 11}] (* _Zerinvary Lajos_, Jul 08 2009 *)
%Y A001145 Cf. A001155, A005150, A006751, A006715, A001140, A001141, A001143, A001151, A001154.
%K A001145 nonn,base,easy,nice
%O A001145 1,1
%A A001145 _N. J. A. Sloane_