%I #17 Jul 11 2023 17:49:37
%S 21,38,265,4109,65553,262163,1048597,67108891,274877906983,
%T 4503599627370549,73786976294838206531,75557863725914323419213,
%U 302231454903657293676623,5192296858534827628530496329220209,10889035741470030830827987437816582766726,95780971304118053647396689196894323976171195136475313
%N Numbers of the form 2^k + k + 1 that are the product of two distinct primes.
%e 21 = 3 * 7 = 2^4 + 4 + 1
%t f[n_]:=Last/@FactorInteger[n]=={1,1};Select[Array[2^#+#+1&,140,0],f[ # ]&]
%t Select[Table[2^k+k+1,{k,0,200}],PrimeNu[#]==PrimeOmega[#]==2&] (* _Harvey P. Dale_, Jul 11 2023 *)
%o (PARI) is(n) = my(f = factor(n), e = logint(n, 2)); f[,2] == [1, 1]~ && n == 1<<e + e + 1 \\ _David A. Corneth_, May 27 2023
%Y Cf. A005126, A053698, A061421, A174969, A176069, A176070.
%K nonn
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, Apr 07 2010
%E Name corrected by _David A. Corneth_, May 27 2023