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 A210506 #11 Dec 15 2021 19:00:27 %S A210506 2,5,11,13,331,599,18839,23747,24371,29339,32141,67421 %N A210506 Numbers k such that (11^k - 2^k)/9 is prime. %C A210506 All terms are prime. %C A210506 a(13) > 10^5. %t A210506 Select[ Prime[ Range[1, 100000] ], PrimeQ[ (11^# - 2^#)/9 ]& ] %o A210506 (PARI) is(n)=isprime((11^n-2^n)/9) \\ _Charles R Greathouse IV_, Feb 17 2017 %Y A210506 Cf. A004063, A028491, A057468, A059801, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032. %K A210506 hard,more,nonn %O A210506 1,1 %A A210506 _Robert Price_, Jan 25 2013