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 A092562 #24 Jun 18 2022 04:04:43
%S A092562 9,33,65,129,2049,4097,8193,131073,524289,1048577,8388609,268435457,
%T A092562 2147483649,4294967297,1099511627777,8796093022209,
%U A092562 2305843009213693953,18446744073709551617,604462909807314587353089,4951760157141521099596496897
%N A092562 Semiprimes of the form 2^k + 1.
%H A092562 Amiram Eldar, <a href="/A092562/b092562.txt">Table of n, a(n) for n = 1..40</a> (terms 1..30 from Vincenzo Librandi)
%F A092562 a(n) = A000051(A092559(n)). - _Amiram Eldar_, Jun 18 2022
%e A092562 2049 is a member because 2049 = 2^11+1 = 3*683.
%t A092562 Select[Table[2^n + 1, {n, 100}], PrimeOmega[#] == 2&] (* _Vincenzo Librandi_, Sep 21 2012 *)
%o A092562 (Magma) IsSemiprime:=func<n | &+[d[2]: d in Factorization(n)] eq 2>; [s: n in [2..100] | IsSemiprime(s) where s is 2^n+1]; // _Vincenzo Librandi_, Sep 21 2012
%Y A092562 Corresponding k: A092559.
%Y A092562 Cf. A000051, A092558, A092561.
%K A092562 nonn
%O A092562 1,1
%A A092562 _Zak Seidov_, Feb 27 2004