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A249627 Product of the lowest and highest prime factors of n-th repunit A002275(n).

%I A249627 #17 Aug 11 2024 14:41:34
%S A249627 121,111,1111,11111,111,1111111,1507,1001001,100001,11111111111,29703,
%T A249627 14064697609,10000001,8718483,64705883,11111111111111111,1001001,
%U A249627 1234567901234567900987654320987654321,307571,32516067,5645629,123456790123456790123454320987654320987654321
%N A249627 Product of the lowest and highest prime factors of n-th repunit A002275(n).
%H A249627 Chai Wah Wu, <a href="/A249627/b249627.txt">Table of n, a(n) for n = 2..322</a>
%H A249627 P. De Geest, <a href="https://www.worldofnumbers.com/repunits.htm">Repunits and Their Factors</a>
%e A249627 Highest and lowest prime factors of 111111 are 3 and 37, so the sixth term is 111.
%t A249627 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 *)
%o A249627 (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
%o A249627 (Python)
%o A249627 from sympy import factorint
%o A249627 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
%Y A249627 Cf. A002275.
%K A249627 nonn,base
%O A249627 2,1
%A A249627 _Jacob Vecht_, Nov 02 2014
%E A249627 More terms from _Derek Orr_, Nov 02 2014