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A221373 A two-digit Look-and-Say sequence starting with 99: each term summarizes the increasing two-digit substrings of the previous term.

%I A221373 #10 Feb 16 2025 08:33:19
%S A221373 99,199,119199,111219191199,311112319121291199,
%T A221373 411312219121123129231291199,311512113219221122223229331141291192199,
%U A221373 511312113114115319421522123229231232133141151191292193199,611412313214315419521222323229631232133241142251152153191292193194199
%N A221373 A two-digit Look-and-Say sequence starting with 99: each term summarizes the increasing two-digit substrings of the previous term.
%C A221373 a(22) is the first term containing a zero; this is due to the fact that a(21) is the first term having exactly 10 occurrences of a two-digit number, namely 10 x 32.
%H A221373 Reinhard Zumkeller, <a href="/A221373/b221373.txt">Table of n, a(n) for n = 0..1000</a>
%H A221373 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LookandSaySequence.html">Look and Say Sequence</a>
%H A221373 Wikipedia, <a href="http://en.wikipedia.org/wiki/Look-and-say_sequence">Look-and-say sequence</a>
%H A221373 Reinhard Zumkeller, <a href="/A209234/a209234.hs.txt">Haskell program for two-digit Look-and-Say sequences</a>
%e A221373 a(0) = 11: 1x99 --> a(1)=199;
%e A221373 a(1) = 199: 1x19 and 1x99 --> a(2)=119199;
%e A221373 a(2) = 119199: 1x11, 2x19, 1x91 and 1x99 --> a(3)=111219191199;
%e A221373 a(3) = 111219191199: 3x11, 1x12, 3x19, 1x21, 2x91 and 1x99 --> a(4)=311112319121291199.
%o A221373 (Haskell) -- See Link.
%Y A221373 Cf. A005151, A047842.
%Y A221373 Cf. A209234 (start=10), A209233 (start=11), A221368 (start=12), A221369 (start=13), A221372 (start=19).
%K A221373 nonn,base
%O A221373 0,1
%A A221373 _Reinhard Zumkeller_, Jan 13 2013