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Largest prime factor of prime(n)-th repunit number.
4

%I #20 Apr 26 2022 14:16:37

%S 11,37,271,4649,513239,265371653,5363222357,1111111111111111111,

%T 11111111111111111111111,77843839397,57336415063790604359,

%U 2212394296770203368013,201763709900322803748657942361

%N Largest prime factor of prime(n)-th repunit number.

%C The sequence of repunit primes is a subsequence of this sequence.

%H <a href="/A147556/b147556.txt">Table of n, a(n) for n = 1..70</a>

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/repunit/">Factorizations of 11...11 (Repunit)</a>.

%F a(n) = A003020(A000040(n)) = A006530(A002275(A000040(n))) = A006530(A019328(A000040(n))). - _Ray Chandler_, May 11 2017

%e Prime(15)=47 and (10^47-1)/9 = 35121409*316362908763458525001406154038726382279, so a(15)=316362908763458525001406154038726382279.

%t Table[FactorInteger[FromDigits[PadRight[{},n,1]]][[-1,1]],{n,Prime[ Range[15]]}] (* _Harvey P. Dale_, Feb 23 2016 *)

%Y Cf. A000040, A002275, A003020, A004022, A006530, A019328, A147555.

%K nonn

%O 1,1

%A _Farideh Firoozbakht_, Dec 26 2008

%E Edited by _Ray Chandler_, Apr 06 2011

%E terms to a(66) in b-file from _Ray Chandler_, May 11 2017

%E a(67)-a(70) in b-file from _Max Alekseyev_, Apr 26 2022