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 A002958 M0870 #37 Oct 21 2023 01:07:51
%S A002958 2,3,8,12,15,27,48,89,137,666,1383,1530,2102,8868,95031,111768,130200,
%T A002958 341540
%N A002958 Numbers k such that 2*25^k - 1 is prime.
%D A002958 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%D A002958 C. R. Zarnke and H. C. Williams, Computer determination of some large primes, pp. 563-570 in Proceedings of the Louisiana Conference on Combinatorics, Graph Theory and Computer Science. Vol. 2, edited R. C. Mullin et al., 1971.
%t A002958 Do[m = n; If[PrimeQ[2*25^n - 1], Print[n]], {n, 1, 10^3}]
%t A002958 Select[Range[0, 5000], PrimeQ[(2*25^# - 1)] &] (* _Vincenzo Librandi_, Sep 25 2012 *)
%o A002958 (PARI) is(n)=ispseudoprime(2*25^n-1) \\ _Charles R Greathouse IV_, Jun 13 2017
%K A002958 nonn,hard,more
%O A002958 1,1
%A A002958 _N. J. A. Sloane_, _Simon Plouffe_
%E A002958 a(10) from _Robert G. Wilson v_, Nov 02 2000
%E A002958 a(11)-a(13) from _Vincenzo Librandi_, Sep 25 2012
%E A002958 a(14)-a(17) (from A120375) from _Joerg Arndt_, Jun 15 2020
%E A002958 a(18) (from A120375) by _Jorge Coveiro_, Jun 20 2020