This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A147556 #20 Apr 26 2022 14:16:37
%S A147556 11,37,271,4649,513239,265371653,5363222357,1111111111111111111,
%T A147556 11111111111111111111111,77843839397,57336415063790604359,
%U A147556 2212394296770203368013,201763709900322803748657942361
%N A147556 Largest prime factor of prime(n)-th repunit number.
%C A147556 The sequence of repunit primes is a subsequence of this sequence.
%H A147556 <a href="/A147556/b147556.txt">Table of n, a(n) for n = 1..70</a>
%H A147556 Makoto Kamada, <a href="https://stdkmd.net/nrr/repunit/">Factorizations of 11...11 (Repunit)</a>.
%F A147556 a(n) = A003020(A000040(n)) = A006530(A002275(A000040(n))) = A006530(A019328(A000040(n))). - _Ray Chandler_, May 11 2017
%e A147556 Prime(15)=47 and (10^47-1)/9 = 35121409*316362908763458525001406154038726382279, so a(15)=316362908763458525001406154038726382279.
%t A147556 Table[FactorInteger[FromDigits[PadRight[{},n,1]]][[-1,1]],{n,Prime[ Range[15]]}] (* _Harvey P. Dale_, Feb 23 2016 *)
%Y A147556 Cf. A000040, A002275, A003020, A004022, A006530, A019328, A147555.
%K A147556 nonn
%O A147556 1,1
%A A147556 _Farideh Firoozbakht_, Dec 26 2008
%E A147556 Edited by _Ray Chandler_, Apr 06 2011
%E A147556 terms to a(66) in b-file from _Ray Chandler_, May 11 2017
%E A147556 a(67)-a(70) in b-file from _Max Alekseyev_, Apr 26 2022