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 A228026 #38 Nov 17 2023 07:35:02
%S A228026 7,19,67,4099,65539,262147,268435459,1073741827,
%T A228026 19342813113834066795298819
%N A228026 Primes of the form 4^k + 3.
%H A228026 Vincenzo Librandi, <a href="/A228026/b228026.txt">Table of n, a(n) for n = 1..16</a>
%F A228026 a(n) = 4^A089437(n) + 3. - _Elmo R. Oliveira_, Nov 14 2023
%e A228026 67 is a term because 4^3 + 3 = 67 is prime.
%t A228026 Select[Table[4^n + 3, {n, 0, 200}], PrimeQ]
%o A228026 (Magma) [a: n in [0..200] | IsPrime(a) where a is 4^n+3];
%Y A228026 Cf. A089437 (associated k).
%Y A228026 Cf. Primes of the form r^k + h: A092506 (r=2, h=1), A057733 (r=2, h=3), A123250 (r=2, h=5), A104066 (r=2, h=7), A104070 (r=2, h=9), A057735 (r=3, h=2), A102903 (r=3, h=4), A102870 (r=3, h=8), A102907 (r=3, h=10), A290200 (r=4, h=1), this sequence (r=4, h=3), A228027 (r=4, h=9), A182330 (r=5, h=2), A228029 (r=5, h=6), A102910 (r=5, h=8), A182331 (r=6, h=1), A104118 (r=6, h=5), A104115 (r=6, h=7), A104065 (r=7, h=4), A228030 (r=7, h=6), A228031 (r=7, h=10), A228032 (r=8, h=3), A228033 (r=8, h=5), A144360 (r=8, h=7), A145440 (r=8, h=9), A228034 (r=9, h=2), A159352 (r=10, h=3), A159031 (r=10, h=7).
%K A228026 nonn,easy
%O A228026 1,1
%A A228026 _Vincenzo Librandi_, Aug 11 2013
%E A228026 Cross-references corrected by _Robert Price_, Aug 01 2017