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A022481
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Describe previous term from the right (method B - initial term is 1).
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11
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1, 11, 12, 2111, 1321, 11213111, 1331112112, 211221133211, 12213212221221, 11221123112131112211, 122213311121123121122212, 211123122111312112211332112311
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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COMMENTS
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Method B = 'digit'-indication followed by 'frequency'.
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LINKS
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EXAMPLE
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E.g. the term after 1321 is obtained by saying "1 once, 2 once, 3 once, 1 once", which gives 11213111.
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MATHEMATICA
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a[1]=1; a[n_]:=a[n]=FromDigits[Flatten[Replace[ Replace[ Replace[ Split[ Reverse[IntegerDigits[a[n-1]]]], {x_, y_}->{x, Length[{x, y}]}, {1}], {x_, y_, z_}->{x, Length[{x, y, z}]}, {1}], {x_}->{x, Length[{x}]}, {1}]]]; Array[a, 15] (* Ivan N. Ianakiev, Jun 22 2017 *)
NestList[FromDigits@ Flatten@ Reverse@ Map[{First@ #, Length@ #} &, Split@ IntegerDigits@ #] &, 1, 11] (* Michael De Vlieger, Jun 26 2017 *)
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PROG
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(Haskell)
import Data.List (group, transpose)
a022481 n = a022481_list !! (n-1)
a022481_list = 1 : f [1] :: [Integer] where
f xs = (read $ concatMap show ys) : f ys where
ys = concat $ transpose [map head zss, map length zss]
zss = reverse $ group xs
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CROSSREFS
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KEYWORD
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nonn,base,easy,nice
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AUTHOR
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STATUS
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approved
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