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 A289808 #17 Jun 17 2025 03:00:19
%S A289808 53,701,59021,14348879,31381059581,282429536453,7625597484959,
%T A289808 50031545098999679,1144561273430837494885949696399,
%U A289808 26183890704263137277674192438430182020124319,2120895147045314119491609587512844743630072079
%N A289808 Primes of the form 3^k - 28.
%H A289808 Robert Price, <a href="/A289808/b289808.txt">Table of n, a(n) for n = 1..18</a>
%H A289808 F. Firoozbakht and M. F. Hasler, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL13/Hasler/hasler2.html">Variations on Euclid's formula for Perfect Numbers</a>, JIS 13 (2010) #10.3.1.
%H A289808 Henri and Renaud Lifchitz, <a href="http://www.primenumbers.net/prptop">PRP Records</a>
%H A289808 OpenPFGW Project, <a href="http://sourceforge.net/projects/openpfgw/">Primality Tester</a>
%F A289808 a(n) = 3^A219047(n) - 28. - _Elmo R. Oliveira_, Nov 12 2023
%t A289808 Select[Table[3^k - 28, {k, 4, 100}], PrimeQ[#] &]
%Y A289808 Cf. A000040, A219047 (corresponding k's).
%K A289808 nonn
%O A289808 1,1
%A A289808 _Robert Price_, Sep 02 2017