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%I #16 Jun 02 2014 22:49:16
%S 6,14,15,62,254,511,2047,16382,262142,1048574,8388607,4294967294,
%T 137438953471,562949953421311,576460752303423487,4611686018427387902,
%U 147573952589676412927,9671406556917033397649407,1237940039285380274899124222,158456325028528675187087900671
%N Semiprimes of the form 2^k - 1 or 2^k - 2.
%C Union of A092561 and 2*A000668.
%t Select[Flatten[Table[{2^k - 2, 2^k - 1}, {k, 100}]], PrimeOmega[#] == 2 &] (* _Alonso del Arte_, May 26 2014 *)
%Y Cf. A092561, A000668.
%K nonn
%O 1,1
%A _Juri-Stepan Gerasimov_, May 23 2014
%E More terms from _Alonso del Arte_, May 26 2014