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 A091336 #20 Feb 16 2025 08:32:52
%S A091336 0,1,2,3,4,6,7,11,15,18,23,27
%N A091336 Number of prime divisors of A000058(n)-1 = A000058(0)*...*A000058(n-1).
%C A091336 All numbers less than 2.5*10^15 in Sylvester's sequence are squarefree and no squareful numbers in this sequence are known (Vardi 1991).
%D A091336 Vardi, I. "Are All Euclid Numbers Squarefree?" and "PowerMod to the Rescue." Sections 5.1 and 5.2 in Computational Recreations in Mathematica. Reading, MA: Addison-Wesley, pp. 82-89, 1991.
%H A091336 Jens Kruse Andersen, <a href="http://primerecords.dk/sylvester-factors.htm">Factorization of Sylvester's sequence</a>
%H A091336 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SylvestersSequence.html">Sylvester's sequence</a>
%F A091336 a(n) = A001221(A000058(n)-1) = A001221(A000058(0)*...*A000058(n-1)) = Sum_{i=0..(n-1)} A091335(i).
%t A091336 PrimeNu[NestList[#^2 - # + 1 &, 2, 10] - 1] (* _G. C. Greubel_, May 09 2017 *)
%Y A091336 Cf. A000058, A091335.
%K A091336 hard,more,nonn
%O A091336 0,3
%A A091336 _Max Alekseyev_, Dec 30 2003
%E A091336 One more term from _Max Alekseyev_, Sep 11 2006