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 A000355 #30 Oct 31 2023 15:58:06
%S A000355 3,11,23,29,83,89,131,191,251,431,443,491,509,683,743,809,911,1031,
%T A000355 1049,1103,1223,1229,1289,1409,1451,1511,1583,1811,1889,1931,2003,
%U A000355 2063,2069,2129,2351,2543,2549,2903,2963,2969,3023,3329,3389,3449,3491,3623,3803
%N A000355 Primes p == 3, 9, 11 (mod 20) such that 2p+1 is also prime.
%C A000355 a(n) = (A000353(n)-1)/2. - _Reinhard Zumkeller_, Feb 10 2009
%H A000355 Reinhard Zumkeller, <a href="/A000355/b000355.txt">Table of n, a(n) for n = 1..1000</a>
%H A000355 Robert A. J. Matthews, <a href="https://www.researchgate.net/publication/266728416_Maximally_periodic_reciprocals">Maximally periodic reciprocals</a>, Bull. Institute of Mathematics and Its Applications, vol. 28, p. 147-148, 1992.
%p A000355 q:= p-> irem(p, 20) in {3, 9, 11} and andmap(isprime, [p,2*p+1]):
%p A000355 select(q, [$1..10000])[]; # _Alois P. Heinz_, Oct 31 2023
%t A000355 Select[Prime[Range[1000]], MatchQ[Mod[#, 20], 3|9|11] && PrimeQ[2#+1]&] (* _Jean-François Alcover_, Feb 07 2016 *)
%o A000355 (PARI) is(n)=my(k=n%20); (k==3||k==9||k==11) && isprime(2*n+1) && isprime(n) \\ _Charles R Greathouse IV_, Nov 20 2014
%Y A000355 Subset of A005384.
%Y A000355 Cf. A000353.
%K A000355 nonn,easy
%O A000355 1,1
%A A000355 _Robert A. J. Matthews_
%E A000355 More terms from _Reinhard Zumkeller_, Feb 10 2009