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A221368 A two-digit Look-and-Say sequence starting with 12: each term summarizes the increasing two-digit substrings of the previous term.

%I A221368 #12 Feb 16 2025 08:33:19
%S A221368 12,112,111112,411112,311112141,311112114121131141,
%T A221368 611212113214221231241,211412113114421122123124131132141142161,
%U A221368 611412313414116621122123124331132341242144161,411512213314216321122323224331132133234541142143144261162166
%N A221368 A two-digit Look-and-Say sequence starting with 12: each term summarizes the increasing two-digit substrings of the previous term.
%C A221368 a(36) is the first term containing a zero; this is due to the fact that a(35) is the first term having exactly 10 occurrences of a two-digit number, namely 10 x 42.
%H A221368 Reinhard Zumkeller, <a href="/A221368/b221368.txt">Table of n, a(n) for n = 0..1000</a>
%H A221368 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LookandSaySequence.html">Look and Say Sequence</a>
%H A221368 Wikipedia, <a href="http://en.wikipedia.org/wiki/Look-and-say_sequence">Look-and-say sequence</a>
%H A221368 Reinhard Zumkeller, <a href="/A209234/a209234.hs.txt">Haskell program for two-digit Look-and-Say sequences</a>
%e A221368 a(0) = 12: 1 x 12 --> a(1) = 112;
%e A221368 a(1) = 112: 1 x 11 ana 1 x 12 --> a(2) = 111112;
%e A221368 a(2) = 111112: 4 x 11 and 1 x 12 --> a(4) = 411112;
%e A221368 a(3) = 411112: 3 x 11, 1 x 12 and 1 x 41 --> a(4) = 311112141.
%o A221368 (Haskell) -- See Link.
%Y A221368 Cf. A005151, A047842.
%Y A221368 Cf. A209234 (start=10), A209233 (start=11), A221369 (start=13), A221372 (start=19), A221373 (start=99).
%K A221368 nonn,base
%O A221368 0,1
%A A221368 _Reinhard Zumkeller_, Jan 13 2013