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 A147555 #25 Jan 17 2019 13:44:08 %S A147555 11,3,41,239,21649,53,2071723,1111111111111111111, %T A147555 11111111111111111111111,3191,2791,2028119,83,173,35121409,107, %U A147555 2559647034361,733,493121,241573142393627673576957439049,12171337159 %N A147555 Smallest prime factor of prime(n)-th repunit number. %C A147555 The sequence of repunit primes is a subsequence of this sequence. %H A147555 Ray Chandler, <a href="/A147555/b147555.txt">Table of n, a(n) for n = 1..96</a> %H A147555 Makoto Kamada, <a href="https://stdkmd.net/nrr/repunit/">Factorizations of 11...11 (Repunit)</a>. %F A147555 a(n) = A067063(A000040(n)) = A020639(A002275(A000040(n))) = A020639(A019328(A000040(n))). - _Ray Chandler_, May 11 2017 %e A147555 prime(15)=47 and (10^47-1)/9 = 35121409*316362908763458525001406154038726382279, so a(15)=35121409. %Y A147555 Cf. A000040, A002275, A004022, A019328, A020639, A067063, A147556. %K A147555 nonn %O A147555 1,1 %A A147555 _Farideh Firoozbakht_, Dec 26 2008 %E A147555 Edited by _Ray Chandler_, Apr 06 2011