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 A338299 #8 Oct 21 2020 22:28:51 %S A338299 19,61,127,331,631,1801,3169,3571,5419,8269,13267,16651,19441,24571, %T A338299 55897,59221,145861,151201,176419,246247,260191,292969,347821,360187, %U A338299 368551,377011,398581,698419,733591,863497,915769,929077,990151,1024921,1155061,1177507,1324681,1372957,1618471,1980469 %N A338299 Primes of the form (p^2+p+1)/3 where p is prime. %C A338299 All terms == 1 (mod 6). %H A338299 Robert Israel, <a href="/A338299/b338299.txt">Table of n, a(n) for n = 1..10000</a> %F A338299 a(n) = (A240971(n)^2 + A240971(n)+1)/3. %F A338299 A240971(n) = (sqrt(12*a(n)-3)-1)/2. %e A338299 a(3) = 127 is prime and 127 = (19^2+19+1)/3 where 19 is prime. %p A338299 A240971:= select(t -> isprime(t) and isprime((t^2+t+1)/3), [seq(i,i=1..1000,6)]): %p A338299 map(t -> (t^2+t+1)/3, A240971); %Y A338299 Cf. A240971. %K A338299 nonn %O A338299 1,1 %A A338299 _J. M. Bergot_ and _Robert Israel_, Oct 21 2020