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URL: https://oeis.org/A022520

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A022520
Describe previous term from the right (method B - initial term is 9).
9
9, 91, 1191, 119112, 21129112, 211291211221, 112212211191211221, 1122122111911322112212, 21112212223112911322112212, 21112212223112912112312311221321
OFFSET
0,1
COMMENTS
Method B = 'digit'-indication followed by 'frequency'.
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 0..21
EXAMPLE
The term after 1191 is obtained by saying "1 once, 9 once, 1 twice", which gives 119112.
PROG
(Haskell)
import Data.List (group, transpose)
a022520 n = a022520_list !! n
a022520_list = 9 : f [9] :: [Integer] where
f xs = (read $ concatMap show ys) : f ys where
ys = concat $ transpose [map head zss, map length zss]
zss = reverse $ group xs
-- Reinhard Zumkeller, Jan 26 2014
CROSSREFS
KEYWORD
nonn,base,easy,nice
EXTENSIONS
More terms from Patrick De Geest, Jun 15 1999
STATUS
approved