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 A242866 #19 Sep 03 2023 10:10:03 %S A242866 6,10,34,514,131074,4294967297,18446744073709551617, %T A242866 340282366920938463463374607431768211457, %U A242866 115792089237316195423570985008687907853269984665640564039457584007913129639937 %N A242866 Union of 2*A019434 and the semiprimes in A000215. %C A242866 The old definition was "Semiprimes of the form 2^(2^k) + 1 or 2^(2^k) + 2 for some k >= 0", but that does not include 10. So I replaced the old definition with the old comment, which seems a better fit. Question: is the sequence defined by the old definition in the OEIS? If not it should be added. - _N. J. A. Sloane_, Sep 03 2023 %H A242866 Wilfrid Keller, <a href="http://www.prothsearch.com/fermat.html">Prime factors k.2^n + 1 of Fermat numbers F_m</a> %Y A242866 Cf. A000215, A019434, A242832. %K A242866 nonn %O A242866 1,1 %A A242866 _Juri-Stepan Gerasimov_, May 24 2014 %E A242866 Definition edited by _N. J. A. Sloane_, Sep 02 2023