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 A002959 M0979 #31 Oct 21 2023 23:47:12
%S A002959 1,2,4,5,14,24,29,36,46,80,474,1018,5180,22581,41649,52744,114564,
%T A002959 147454,174180
%N A002959 Numbers k such that 2*7^k - 1 is prime.
%D A002959 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%D A002959 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 A002959 Do[ If[ PrimeQ[ 2*7^n - 1 ], Print[n] ], {n, 1, 10000} ]
%o A002959 (PARI) is(n)=ispseudoprime(2*7^n-1) \\ _Charles R Greathouse IV_, Feb 17 2017
%K A002959 nonn,hard,more
%O A002959 1,2
%A A002959 _N. J. A. Sloane_
%E A002959 More terms from _Robert G. Wilson v_, Jan 05 2001
%E A002959 a(14)-a(19) from _Predrag Kurtovic_, May 24 2015