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 A242115 #23 Nov 27 2019 05:32:44
%S A242115 159,895,2047,4607,10239,49151,4718591,20971519,838860799,
%T A242115 137438953471,5085241278463,21440476741631,340010386766614455386111,
%U A242115 96714065569170333976494079,3288278229351791355200798719,111414603535684224740921180159,15370263527767281493147526365183
%N A242115 Woodall semiprimes: Semiprimes of the form n*2^n - 1.
%C A242115 The n-th Woodall number is Wn = n*2^n - 1.
%C A242115 If Wn is semiprime, it is in the sequence.
%H A242115 Amiram Eldar, <a href="/A242115/b242115.txt">Table of n, a(n) for n = 1..47</a> (terms 1..26 from K. D. Bajpai)
%F A242115 a(n) = A003261(A242273(n)). - _Amiram Eldar_, Nov 27 2019
%e A242115 a(1) = 159 = (5*2^5 - 1) is 5th Woodall number and 159 = 3*53 which is semiprime.
%e A242115 a(2) = 895 = (7*2^7 - 1) is 7th Woodall number and 895 = 5*179 which is semiprime.
%p A242115 with(numtheory): A242115:= proc(); if bigomega(x*2^x-1)=2 then RETURN (x*2^x-1); fi; end: seq(A242115 (),x=1..200);
%t A242115 Select[Table[n*2^n-1,{n,100}],PrimeOmega[#]==2&] (* _Harvey P. Dale_, Jan 03 2019 *)
%o A242115 (PARI) for(n=1, 1000, if(bigomega(n*2^n-1)==2, print1(n*2^n-1, ", "))) \\ _Colin Barker_, May 07 2014
%Y A242115 Cf. A001358, A002234, A003261, A050918, A242273.
%K A242115 nonn
%O A242115 1,1
%A A242115 _K. D. Bajpai_, May 04 2014