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 A023209 #30 Sep 08 2022 08:44:47 %S A023209 3,5,11,13,19,23,31,41,53,59,73,79,89,101,103,109,131,139,151,173,179, %T A023209 181,191,199,223,229,241,251,269,283,293,311,331,349,353,373,383,389, %U A023209 409,431,433,439,509,521,541,563,593,599,619,643,661,683,709,719,733,739,761 %N A023209 Primes p such that 3p + 4 is also prime. %C A023209 In order for 3p + 4 to also be in the sequence, it is a necessary but not sufficient condition that p is not congruent to 7 modulo 10. - _Alonso del Arte_, Nov 08 2018 %H A023209 Harvey P. Dale, <a href="/A023209/b023209.txt">Table of n, a(n) for n = 1..1000</a> %e A023209 3 and 3 * 3 + 4 = 13 are both prime, so 3 is in the sequence. %e A023209 5 and 3 * 5 + 4 = 19 are both prime, so 5 is in the sequence. %e A023209 7 is prime but 3 * 7 + 4 = 25 = 5^2, which is not prime, so 7 is not in the sequence. %t A023209 Select[Prime[Range[500]], PrimeQ[3# + 4] &] (* _Harvey P. Dale_, Mar 09 2014 *) %o A023209 (Magma) [n: n in [0..1000] | IsPrime(n) and IsPrime(3*n+4)]; // _Vincenzo Librandi_, Nov 18 2010 %o A023209 (PARI) isok(p) = isprime(p) && isprime(3*p+4); \\ _Michel Marcus_, Nov 09 2018 %Y A023209 Cf. A258261 (3p - 4). %K A023209 nonn,easy %O A023209 1,1 %A A023209 _David W. Wilson_ %E A023209 Name adjusted by _Alonso del Arte_, Nov 08 2018