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 A156983 #20 Nov 08 2023 12:09:21
%S A156983 23,29,37,53,149,277,2069,32789,65557,524309,17592186044437,
%T A156983 281474976710677,2251799813685269,4503599627370517,
%U A156983 2305843009213693973,11692013098647223345629478661730264157247460343829
%N A156983 Primes of the form 2^k + 21.
%F A156983 a(n) = 2^A057201(n) + 21. - _Elmo R. Oliveira_, Nov 08 2023
%e A156983 23 = 2^1 + 21 is in the sequence; 29 = 2^3 + 21 is in the sequence.
%t A156983 Delete[Union[Table[If[PrimeQ[2^n + 21], 2^n + 21, 0], {n, 1, 500}]],1]
%o A156983 (Magma) [ a: n in [1..200] | IsPrime(a) where a is 2^n+21 ]; // _Vincenzo Librandi_, Nov 27 2010
%Y A156983 Cf. A000040, A019434 (2^(2^k) + 1), A057201, A057733 (2^k + 3), A123250 (2^k + 5).
%K A156983 nonn
%O A156983 1,1
%A A156983 Edwin Dyke (ed.dyke(AT)btinternet.com), Feb 20 2009
%E A156983 More terms from _Vincenzo Librandi_, Apr 29 2010