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

4, 41, 1141, 114112, 21124112, 211241211221, 112212211141211221, 1122122111411322112212, 21112212223112411322112212, 21112212223112412112312311221321

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• base
• easy
• nice

Comments

Method B = 'digit'-indication followed by 'frequency'.

Examples

			The term after 1141 is obtained by saying "1 once, 4 once, 1 twice", which gives 114112.
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 0..21

Crossrefs

Cf. A022481, A022488, A022514-A022520.

Programs

Haskell

import Data.List (group, transpose)
a022515 n = a022515_list !! n
a022515_list = 4 : f [4] :: [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

Mathematica

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 *)

Extensions

More terms from Patrick De Geest, Jun 15 1999