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 A265487 #21 Sep 08 2022 08:46:14 %S A265487 1,3,10,18,70,585,921,1943,4635,13543,13803,15938,39004 %N A265487 Numbers k such that 81^k - 9^k - 1 is prime. %C A265487 2*a(n) is in A265481. %C A265487 For k = 1, 3, 10, 18 the corresponding primes are 71, 530711, 12157665455570144399, 22528399544939174261745512577773519. %C A265487 a(n) is not of the form 5*k+2 (divisibility by 11), 9*k+2 (divisibility by 19), 7*k+2*(-1)^k+7 (divisibility by 29), 15*k+2 (divisibility by 31) or 29*k+8 (divisibility by 59). %C A265487 a(14) > 10^5. - _Robert Price_, Apr 21 2020 %e A265487 3 is in the sequence because 81^3 - 9^3 - 1 = 530711 is prime. %t A265487 Select[Range[1000], PrimeQ[81^# - 9^# - 1] &] %o A265487 (Magma) [n: n in [0..500] | IsPrime(81^n-9^n-1)]; %o A265487 (PARI) for(n=1, 1e3, if(ispseudoprime(81^n - 9^n - 1), print1(n, ", "))) \\ _Altug Alkan_, Dec 12 2015 %Y A265487 Cf. similar sequences listed in A265481. %K A265487 nonn,more %O A265487 1,2 %A A265487 _Vincenzo Librandi_, Dec 12 2015 %E A265487 a(9) from _Altug Alkan_, Dec 12 2015 %E A265487 a(10)-a(13) computed from A265481 by _Ray Chandler_, Sep 25 2019