A022518 -id:A022518 - cp's OEIS frontend

A022481 Describe previous term from the right (method B - initial term is 1).

1, 11, 12, 2111, 1321, 11213111, 1331112112, 211221133211, 12213212221221, 11221123112131112211, 122213311121123121122212, 211123122111312112211332112311

Offset: 1

Clark Kimberling

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

			E.g. the term after 1321 is obtained by saying "1 once, 2 once, 3 once, 1 once", which gives 11213111.

Reinhard Zumkeller, Table of n, a(n) for n = 1..24

Cf. A022488, A022514, A022515, A022516, A022517, A022518, A022519, A022520.

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
-- Reinhard Zumkeller, Jan 26 2014

A022481[1]:=1;A022481[n_]:=A022481[n]=FromDigits[Flatten[{First[#],Length[#]}&/@Split[Reverse[IntegerDigits[A022481[n-1]]]]]];Map[A022481,Range[15]] (* Peter J. C. Moses, Apr 22 2013 *)
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 *)

A022488 Describe previous term from the right (method B - initial term is 2).

Original entry on oeis.org

2, 21, 1121, 112112, 21122112, 2112221221, 112211231221, 1122113121122212, 21112312211131122212, 211123123113221131211321, 112131122111311222311231211131211321, 112131122111311321113121123123123113221231112112

Offset: 1

Clark Kimberling

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

			E.g., the term after 1121 is obtained by saying "1 once, 2 once, 1 twice", which gives 112112.

Reinhard Zumkeller, Table of n, a(n) for n = 1..22

Cf. A022481, A022514, A022515, A022516, A022517, A022518, A022519, A022520.

import Data.List (group, transpose)
a022488 n = a022488_list !! (n-1)
a022488_list = 2 : f [2] :: [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, Apr 14 2014

A022488[1]:=2;A022488[n_]:=A022488[n]=FromDigits[Flatten[{First[#],Length[#]}&/@Split[Reverse[IntegerDigits[A022488[n-1]]]]]];Map[A022488,Range[15]] (* Peter J. C. Moses, Apr 22 2013 *)

from re import split
A022488_list, l = [2], '2'
for _ in range(10):
    l = ''.join(d[0]+str(len(d)) for d in split('(0+|1+|2+|3+|4+|5+|6+|7+|8+|9+)',l[::-1]) if d != '')
    A022488_list.append(int(l)) # Chai Wah Wu, Jan 07 2015

from itertools import accumulate, groupby, repeat
def summarize(n, _):
  return int("".join(k+str(len(list(g))) for k, g in groupby(str(n)[::-1])))
def aupton(nn): return list(accumulate(repeat(2, nn), summarize))
print(aupton(12)) # Michael S. Branicky, Feb 21 2021

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A022481 Describe previous term from the right (method B - initial term is 1).

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