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 A156555 #26 Nov 09 2023 11:25:22 %S A156555 5,23,239,10460353199,617673396283943,450283905890997359, %T A156555 36472996377170786399,19383245667680019896796719, %U A156555 67585198634817523235520443624317919,1546132562196033993109383389296863818106322565999 %N A156555 Primes of the form 3^k - 4. %C A156555 The next term, a(11), has 84 digits. - _Harvey P. Dale_, Jul 24 2011 %H A156555 Vincenzo Librandi, <a href="/A156555/b156555.txt">Table of n, a(n) for n = 1..17</a> %H A156555 F. Firoozbakht, 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 A156555 Henri & Renaud Lifchitz, <a href="http://www.primenumbers.net/prptop">PRP Records</a> %H A156555 OpenPFGW Project, <a href="http://sourceforge.net/projects/openpfgw/">Primality Tester</a> %F A156555 a(n) = 3^A058959(n) - 4. - _M. F. Hasler_, Oct 31 2009 %e A156555 a(1) = 3^2 - 4 = 5 is the smallest prime of that form. - _M. F. Hasler_, Oct 31 2009 %t A156555 Select[3^Range[200]-4,PrimeQ] (* _Harvey P. Dale_, Jul 24 2011 *) %o A156555 (PARI) for( k=2,999, is/*pseudo*/prime( p=3^k-4 ) & print1(p", ")) \\ _M. F. Hasler_, Oct 31 2009 %Y A156555 Cf. A000040, A058959 (corresponding k's). %K A156555 nonn %O A156555 1,1 %A A156555 _Vincenzo Librandi_, Feb 10 2009 %E A156555 a(5) corrected by _M. F. Hasler_, Oct 31 2009 %E A156555 a(10) from _Harvey P. Dale_, Jul 24 2011