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A249627
Product of the lowest and highest prime factors of n-th repunit A002275(n).
1
121, 111, 1111, 11111, 111, 1111111, 1507, 1001001, 100001, 11111111111, 29703, 14064697609, 10000001, 8718483, 64705883, 11111111111111111, 1001001, 1234567901234567900987654320987654321, 307571, 32516067, 5645629, 123456790123456790123454320987654320987654321
OFFSET
2,1
EXAMPLE
Highest and lowest prime factors of 111111 are 3 and 37, so the sixth term is 111.
MATHEMATICA
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 *)
PROG
(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
CROSSREFS
Cf. A002275.
Sequence in context: A197817 A152144 A282344 * A202003 A109838 A014734
KEYWORD
nonn,base
AUTHOR
Jacob Vecht, Nov 02 2014
EXTENSIONS
More terms from Derek Orr, Nov 02 2014
STATUS
approved