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 A265483 #19 Sep 08 2022 08:46:14 %S A265483 1,2,4,15,16,24,57,206,284,1290,1722,1862,1866,3271,5306,5474,15401, %T A265483 18729,34757,42842,63930,89967 %N A265483 Numbers k such that 25^k - 5^k - 1 is prime. %C A265483 For k = 1, 2, 4, 15, 16, the corresponding primes are 19, 599, 389999, 931322574584960937499, 23283064365234374999999. %C A265483 a(n) is not of the form 5*m + 3 (divisibility by 11) or 9*m + 10 (divisibility by 19), 7*m + (-1)^m + 7 (divisibility by 29) or 29*m + 27 (divisibility by 59). %C A265483 a(23) > 10^5. - _Robert Price_, Dec 12 2019 %e A265483 4 is in the sequence because 25^4-5^4-1 = 389999 is prime. %t A265483 Select[Range[6000], PrimeQ[25^# - 5^# - 1] &] %o A265483 (Magma) [n: n in [0..300] | IsPrime(25^n-5^n-1)]; %o A265483 (PARI) is(n)=ispseudoprime(25^n - 5^n - 1) \\ _Anders Hellström_, Dec 11 2015 %Y A265483 Cf. similar sequences listed in A265481. %K A265483 nonn,more %O A265483 1,2 %A A265483 _Vincenzo Librandi_, Dec 11 2015 %E A265483 a(17)-a(22) from _Robert Price_, Dec 12 2019