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 A219047 #18 Nov 12 2023 13:03:04
%S A219047 4,6,10,15,22,24,27,35,63,91,95,96,124,132,220,280,338,372,432,568,
%T A219047 692,738,1144,1168,1698,2080,2138,2710,2895,2984,3536,3816,4462,4972,
%U A219047 6588,6666,10350,58991,68854,145806,163500,196192
%N A219047 Numbers k such that 3^k - 28 is prime.
%C A219047 a(43) > 2*10^5. - _Robert Price_, Dec 10 2013
%e A219047 3^4 - 28 = 53 (prime), so 4 is in the sequence.
%t A219047 Do[If[PrimeQ[3^n - 28], Print[n]], {n, 10000}]
%o A219047 (PARI) is(n)=isprime(3^n-28) \\ _Charles R Greathouse IV_, Feb 17 2017
%Y A219047 Cf. Sequences of numbers k such that 3^k + m is prime:
%Y A219047 (m = 2) A051783, (m = -2) A014224, (m = 4) A058958, (m = -4) A058959,
%Y A219047 (m = 8) A217136, (m = -8) A217135, (m = 10) A217137, (m = -10) A217347,
%Y A219047 (m = 14) A219035, (m = -14) A219038, (m = 16) A205647, (m = -16) A219039,
%Y A219047 (m = 20) A219040, (m = -20) A219041, (m = 22) A219042, (m = -22) A219043,
%Y A219047 (m = 26) A219044, (m = -26) A219045, (m = 28) A219046, (m = -28) A219047,
%Y A219047 (m = 32) A219048, (m = -32) A219049, (m = 34) A219050, (m = -34) A219051. Note that if m is a multiple of 3, 3^k + m is also a multiple of 3 (for k greater than 0), and as such isn't prime.
%K A219047 nonn,more
%O A219047 1,1
%A A219047 _Nicolas M. Perrault_, Nov 10 2012
%E A219047 a(37)-a(42) from _Robert Price_, Dec 10 2013