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A022470 Describe the previous term! (method B - initial term is 2). 15
2, 21, 2111, 2113, 211231, 2112213111, 211222113113, 21122312311231, 2112223111213112213111, 21122331132111311222113113, 211222321231211331122312311231, 21122331211121311121123212223111213112213111, 21122232112113211131132112213121112331132111311222113113 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Peter J. C. Moses, Table of n, a(n) for n = 1..23

EXAMPLE

E.g., the term after 2113 is obtained by saying "2 once, 1 twice, 3 once", which gives 211231.

MATHEMATICA

a[1] = 2; a[n_] := a[n] = FromDigits[Flatten[{First[#], Length[#]} & /@ Split[IntegerDigits[a[n - 1]]]]]; Map[a, Range[1, 23]] (* Peter J. C. Moses, Mar 22 2013 *)

PROG

(Python)

from itertools import accumulate, groupby, repeat

def summarize(n, _):

  return int("".join(k+str(len(list(g))) for k, g in groupby(str(n))))

def aupton(nn): return list(accumulate(repeat(2, nn), summarize))

print(aupton(13)) # Michael S. Branicky, Feb 21 2021

CROSSREFS

Cf. A007651, A022499, A022500-A022505.

Cf. A006751 (method A).

Sequence in context: A264066 A052157 A050204 * A080815 A276654 A114846

Adjacent sequences:  A022467 A022468 A022469 * A022471 A022472 A022473

KEYWORD

nonn,base,easy,nice

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified May 16 12:25 EDT 2021. Contains 343947 sequences. (Running on oeis4.)