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 A155900 #20 Jan 21 2023 18:01:30
%S A155900 1,2,3,4,5,7,8,9,13,16,17,19,27,31,32,49,61,89,107,127,521,607,1279,
%T A155900 2203,2281,3217
%N A155900 Numbers k such that Omega(k) = Omega(2^k-1), where Omega(k) is the number of prime factors of k counted with multiplicity (A001222).
%C A155900 Mersenne prime exponents A000043 are a subsequence, with Omega(p)=Omega(2^p-1)=1.
%H A155900 Davar55 et al., <a href="http://www.mersenneforum.org/showthread.php?t=11418">"Mersenne-Like", discussion on mersenneforum.org</a>, Jan 27 2009.
%F A155900 {n: A046051(n) = A001222(n)}. - _R. J. Mathar_, Mar 14 2009
%t A155900 Select[Range[200],PrimeOmega[#]==PrimeOmega[2^#-1]&] (* _Harvey P. Dale_, Apr 21 2012 *)
%o A155900 (PARI) for( i=1,999, bigomega(2^i-1)==bigomega(i) & print1(i","))
%Y A155900 Cf. A000043, A000225, A001222, A046051.
%K A155900 nonn,more
%O A155900 1,2
%A A155900 _M. F. Hasler_, Feb 01 2009
%E A155900 a(21)-a(22) from _Amiram Eldar_, Feb 23 2021
%E A155900 a(23)-a(26) from _Daniel Suteu_, Jan 21 2023