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 A087885 #45 Jun 06 2021 17:19:02
%S A087885 0,1,3,17,143,261,551,2285,18731,18995,19751,62067,98051,169727,442281
%N A087885 Numbers k such that 5^k + 2 is a prime.
%C A087885 Terms <= 551 correspond to certified primes.
%C A087885 a(15) > 2*10^5. - _Robert Price_, Jan 16 2015
%H A087885 Henri & Renaud Lifchitz, <a href="http://www.primenumbers.net/prptop/searchform.php?form=5%5En%2B2&action=Search">PRP Records</a>.
%e A087885 a(3)=3 is a term because 5^3 + 2 = 127 is a prime.
%e A087885 5^17 + 2 = 762939453127 is prime, hence 17 is a term.
%t A087885 Do[If[PrimeQ[5^n + 2], Print[n]], {n, 1, 10000}] (* _Ryan Propper_, Jun 17 2005 *)
%o A087885 (PARI) for(n=0, 10^5, if(ispseudoprime(5^n+2), print1(n, ", "))) \\ _Felix Fröhlich_, Jun 04 2014
%Y A087885 Cf. A051783 (3^n + 2 is prime).
%K A087885 hard,nonn
%O A087885 1,3
%A A087885 _Donald S. McDonald_, Oct 13 2003
%E A087885 a(7)-a(8) from _Ryan Propper_, Jun 17 2005
%E A087885 a(9)-a(12) found by Mike Oakes in 2003. - _Alexander Adamchuk_, Mar 02 2008
%E A087885 Edited by _Ray Chandler_, Jul 27 2011
%E A087885 a(13) from _Ray Chandler_, Jul 28 2011
%E A087885 a(14) from _Robert Price_, Jan 16 2015
%E A087885 a(15) from _Paul Bourdelais_, Jan 28 2021