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A249627
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Product of the lowest and highest prime factors of n-th repunit A002275(n).
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1
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121, 111, 1111, 11111, 111, 1111111, 1507, 1001001, 100001, 11111111111, 29703, 14064697609, 10000001, 8718483, 64705883, 11111111111111111, 1001001, 1234567901234567900987654320987654321, 307571, 32516067, 5645629, 123456790123456790123454320987654320987654321
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OFFSET
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2,1
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LINKS
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EXAMPLE
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Highest and lowest prime factors of 111111 are 3 and 37, so the sixth term is 111.
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MATHEMATICA
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plh[n_]:=Module[{fi=FactorInteger[FromDigits[PadRight[{}, n, 1]]]}, fi[[1, 1]]fi[[-1, 1]]]; Array[plh, 30, 2] (* Harvey P. Dale, May 04 2021 *)
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PROG
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(PARI) for(n=2, 20, p=(10^n-1)/9; print1(factor(p)[1, 1]*factor(p)[#factor(p)[, 1], 1], ", ")) \\ Derek Orr, Nov 02 2014
(Python)
from sympy import factorint
A249627_list = [min(fs)*max(fs) for fs in (factorint((10**n-1)//9) for n in range(2, 31))] # Chai Wah Wu, Nov 04 2019
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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