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A022515 Describe previous term from the right (method B - initial term is 4).

%I A022515 #15 Oct 06 2019 16:55:15
%S A022515 4,41,1141,114112,21124112,211241211221,112212211141211221,
%T A022515 1122122111411322112212,21112212223112411322112212,
%U A022515 21112212223112412112312311221321
%N A022515 Describe previous term from the right (method B - initial term is 4).
%C A022515 Method B = 'digit'-indication followed by 'frequency'.
%H A022515 Reinhard Zumkeller, <a href="/A022515/b022515.txt">Table of n, a(n) for n = 0..21</a>
%e A022515 The term after 1141 is obtained by saying "1 once, 4 once, 1 twice", which gives 114112.
%t A022515 A022515[1]:=4;A022515[n_]:=A022515[n]=FromDigits[Flatten[{First[#],Length[#]}&/@Split[Reverse[IntegerDigits[A022515[n-1]]]]]];Map[A022515,Range[15]] (* _Peter J. C. Moses_, Apr 22 2013 *)
%o A022515 (Haskell)
%o A022515 import Data.List (group, transpose)
%o A022515 a022515 n = a022515_list !! n
%o A022515 a022515_list = 4 : f [4] :: [Integer] where
%o A022515    f xs = (read $ concatMap show ys) : f ys where
%o A022515           ys = concat $ transpose [map head zss, map length zss]
%o A022515           zss = reverse $ group xs
%o A022515 -- _Reinhard Zumkeller_, Jan 26 2014
%Y A022515 Cf. A022481, A022488, A022514-A022520.
%K A022515 nonn,base,easy,nice
%O A022515 0,1
%A A022515 _N. J. A. Sloane_
%E A022515 More terms from _Patrick De Geest_, Jun 15 1999