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 A229850 #20 Feb 16 2025 08:33:20 %S A229850 0,0,0,0,0,1,1,1,1,0,3,2 %N A229850 Number of prime factors congruent to 1 mod 3 that divide the Fermat number 2^(2^n) + 1. %C A229850 a(n) < A046052(n) because all Fermat numbers greater than 3 are equal to 2 (mod 3). %C A229850 a(n) = 1 if A046052(n) = 2. %C A229850 If A046052(n) = 3, then a(n) = 0 or 2. %C A229850 a(n) <= A228846(n) - n - 1 for n = 0 to 11. %D A229850 M. Krizek, F. Luca, L. Somer, 17 Lectures on Fermat Numbers: From Number Theory to Geometry, CMS Books in Mathematics, vol. 9, Springer-Verlag, New York, 2001, pp. 61-63, 65-66. %H A229850 Wilfrid Keller, <a href="http://www.prothsearch.com/fermat.html">Fermat factoring status</a> %H A229850 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/FermatNumber.html">Fermat Number</a> %Y A229850 Cf. A000215, A002476, A023394, A046052, A229854. %K A229850 nonn,hard,more %O A229850 0,11 %A A229850 _Arkadiusz Wesolowski_, Oct 01 2013