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 A087274 #17 Jul 12 2024 10:16:42
%S A087274 4,3,1,5,7,3,6,10,4,5,15,4,11,6,20,3,24,9,26,28,5,7,3,19,21,8,11,9,13,
%T A087274 7,43,45,27,8,4,49,17,4,54,6,57,7,13,10,12,9,66,19,11,14,4,72,42,10,
%U A087274 44,22,26,12,6,47,7,5,89,91,15,7,20,9,98,32,16,5,10,4,104,9,21,35,14,63,12,22
%N A087274 Prime index of the largest prime factor of 3*prime(n)+1.
%H A087274 Amiram Eldar, <a href="/A087274/b087274.txt">Table of n, a(n) for n = 1..10000</a>
%F A087274 a(n) = A000720(A006530(1+3*A000040(n))).
%F A087274 a(n) = A000720(A087273(n)). - _Amiram Eldar_, Jul 12 2024
%e A087274 n=10: prime(10)=29, max-p-factor(88)=11, pi(11)=5=a(10)<n;
%e A087274 n=11: prime(11)=31, max-p-factor(94)=47, pi(47)=15=a(11)>n;
%t A087274 ffi[x_] := Flatten[FactorInteger[x]]; ma[x_] := Part[Reverse[ffi[x]], 2]; Table[PrimePi[ma[3*Prime[w]+1]], {w, 1, 100}]
%o A087274 (PARI) a(n) = primepi(vecmax(factor(3*prime(n)+1)[, 1])); \\ _Michel Marcus_, Mar 27 2020
%Y A087274 Cf. A000720, A006530, A087272, A087273.
%K A087274 nonn
%O A087274 1,1
%A A087274 _Labos Elemer_, Sep 18 2003