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A022470
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Describe the previous term! (method B - initial term is 2).
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15
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2, 21, 2111, 2113, 211231, 2112213111, 211222113113, 21122312311231, 2112223111213112213111, 21122331132111311222113113, 211222321231211331122312311231, 21122331211121311121123212223111213112213111, 21122232112113211131132112213121112331132111311222113113
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OFFSET
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1,1
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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 2113 is obtained by saying "2 once, 1 twice, 3 once", which gives 211231.
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MATHEMATICA
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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 *)
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PROG
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(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))
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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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