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%I #14 Dec 17 2021 06:02:46
%S 3,13,1311,211311,21132112,122112132112,122112131112212211,
%T 2122112231131112212211,21221122311321132221221112,
%U 12312211321321121321132221221112
%N Describe previous term from the right (method A - initial term is 3).
%C Method A = 'frequency' followed by 'digit'-indication.
%H Reinhard Zumkeller, <a href="/A022507/b022507.txt">Table of n, a(n) for n = 0..21</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/LookandSaySequence.html">Look and Say Sequence</a>
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Look-and-say_sequence">Look-and-say sequence</a>
%F a(n+1) = A045918(A004086(a(n))). - _Reinhard Zumkeller_, Mar 02 2014
%e The term after 1311 is obtained by saying "two 1's, one 3, one 1", which gives 211311.
%t A022507[1]:=3;A022507[n_]:=A022507[n]=FromDigits[Flatten[{Length[#],First[#]}&/@Split[Reverse[IntegerDigits[A022507[n-1]]]]]];Map[A022507,Range[15]] (* _Peter J. C. Moses_, Apr 22 2013 *)
%o (Haskell)
%o a022507 n = a022507_list !! n
%o a022507_list = iterate (a045918 . a004086) 3
%o -- _Reinhard Zumkeller_, Mar 02 2014
%Y Cf. A022506, A006711, A022482, A022508-A022513.
%K nonn,base,easy,nice
%O 0,1
%A _N. J. A. Sloane_
%E More terms from _Erich Friedman_
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