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 A102904 #15 Nov 12 2023 09:31:14
%S A102904 23,29,47,101,263,2207,6581,59069,177167,4782989,
%T A102904 984770902183611232901,174449211009120179071170527,
%U A102904 278128389443693511257285776231781,7509466514979724803946715958257567
%N A102904 Primes of the form 3^k + 20.
%C A102904 The sequence of the corresponding k starts 1, 2, 3, 4, 5, 7, 8, 10, 11, 14, 44, 55, 68, 71, 80, 123, 158, 213, 220, 272, 668, 725, 885, 1132, 1677, 2056, ... [_Joerg Arndt_, Jul 19 2012]
%H A102904 Vincenzo Librandi, <a href="/A102904/b102904.txt">Table of n, a(n) for n = 1..23</a>
%F A102904 a(n) = 3^A219040(n) + 20. - _Elmo R. Oliveira_, Nov 12 2023
%t A102904 Select[Table[3^n+20, {n,0,200}],PrimeQ] (* _Vincenzo Librandi_, Jul 19 2012 *)
%o A102904 (Magma) [ a: n in [0..100] | IsPrime(a) where a is 3^n+20 ]; // _Vincenzo Librandi_, Jul 19 2012
%Y A102904 Cf. A000040, A000960, A219040 (corresponding k's).
%K A102904 nonn
%O A102904 1,1
%A A102904 _Roger L. Bagula_, Mar 01 2005