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 A074809 #23 Apr 08 2024 06:55:25
%S A074809 2,23,47,2357,223,35339,214282847,7717859,806801,185176472401,357211,
%T A074809 4967701595369,104364752351,27558919,5269410931806332951,
%U A074809 274784055330749,1191126125288819,178258515898000387,2313161253378144566969023310693,8730041915527145606449758346652473,26293517701186435480644832888393,29890227360205834316383307128051,3858432486690092813,7122852423207105431971,93753283248830261744671
%N A074809 Largest prime factor of A019518, concatenation of first n primes.
%H A074809 Daniel Suteu, <a href="/A074809/b074809.txt">Table of n, a(n) for n = 1..69</a>
%F A074809 a(n) = A006530(A019518(n)). - _Daniel Suteu_, May 26 2022
%e A074809 For n=5: concatenation of {2,3,5,7,11} is 235711 = 7*151*223, largest prime divisor is a(5)=223.
%t A074809 <<NumberTheory`NumberTheoryFunctions` sz[x_] :=FromDigits[Flatten[Table[IntegerDigits[Prime[j]], {j, 1, x}], 1]] Table[Max[PrimeFactorList[sz[w]]], {w, 1, 25}] (* _Labos Elemer_, Mar 18 2005 *)
%t A074809 Table[FactorInteger[FromDigits[Flatten[IntegerDigits/@Prime[ Range[n]]]]][[-1,1]],{n,25}] (* _Harvey P. Dale_, Apr 27 2015 *)
%o A074809 (PARI) a(n) = vecmax(factor(eval(concat(apply(s->Str(s), primes(n)))))[,1]); \\ _Daniel Suteu_, May 26 2022
%Y A074809 Cf. A019518.
%K A074809 nonn,base
%O A074809 1,1
%A A074809 _Jason Earls_, Sep 08 2002
%E A074809 More terms from _Labos Elemer_, Mar 18 2005
%E A074809 Edited by _Charles R Greathouse IV_, Apr 23 2010