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 A005540 M2422 #31 Jul 15 2018 12:04:43 %S A005540 0,1,3,5,7,15,45,95,235,463,733,1437,1583,1677,1803,4163,4765,9219, %T A005540 9959,25477,26059,41539,54195,65057,74977,116589,192289,311835,350767, %U A005540 353635,416337,423253 %N A005540 Numbers k such that 4*3^k - 1 is prime. %D A005540 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A005540 H. C. Williams and C. R. Zarnke, <a href="https://doi.org/10.1090/S0025-5718-1972-0314747-X">Some prime numbers of the forms 2*3^n+1 and 2*3^n-1</a>, Math. Comp., 26 (1972), 995-998. %o A005540 (PARI) is(n)=ispseudoprime(4*3^n-1) \\ _Charles R Greathouse IV_, Feb 20 2017 %K A005540 nonn,hard %O A005540 1,3 %A A005540 _N. J. A. Sloane_ %E A005540 More terms from _Robert G. Wilson v_ and from _Jud McCranie_ %E A005540 More terms from _Borys Jaworski_, Feb 13 2010 %E A005540 0 added by _Vincenzo Librandi_, Sep 26 2012