%I #19 Sep 03 2023 10:10:03

%S 6,10,34,514,131074,4294967297,18446744073709551617,

%T 340282366920938463463374607431768211457,

%U 115792089237316195423570985008687907853269984665640564039457584007913129639937

%N Union of 2*A019434 and the semiprimes in A000215.

%C 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 Wilfrid Keller, <a href="http://www.prothsearch.com/fermat.html">Prime factors k.2^n + 1 of Fermat numbers F_m</a>

%Y Cf. A000215, A019434, A242832.

%K nonn

%O 1,1

%A _Juri-Stepan Gerasimov_, May 24 2014

%E Definition edited by _N. J. A. Sloane_, Sep 02 2023