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 A255581 #33 Mar 06 2015 17:00:24
%S A255581 13,23,29,37,41,43,59,61,67,71,79,89,97,103,109,137,149,173,193,197,
%T A255581 223,227,239,269,271,307,311,313,349,353,383,409,463,467,479,487,491,
%U A255581 521,541,547,571,577,607,613,617,619,653,659,661,691,809,821,823,857
%N A255581 Numbers prime(n) such that prime(n)^2 + prime(n+1)^2 - prime(n+2)^2 is prime.
%e A255581 13 belongs to the sequence as 13 is prime, 13 is the 6th prime number, the 7th prime is 17, the 8th prime is 19, and 13^2 + 17^2 - 19^2 = 97, which is prime.
%e A255581 31 does not belong to the sequence as 31^2 + 37^2 - 41^2 = 649 and 649 is not prime.
%p A255581 A255581:=n->`if`(isprime(ithprime(n)^2+ithprime(n+1)^2-ithprime(n+2)^2), ithprime(n), NULL): seq(A255581(n), n=1..200); # _Wesley Ivan Hurt_, Feb 28 2015
%o A255581 (Octave) p=primes(500); for i=1:100 ris=(p(i))^2+(p(i+1))^2-(p(i+2))^2; if ris>0 if isprime(ris) disp(p(i)); end end end
%o A255581 (PARI) lista(nn) = {forprime(p=2, nn, q = nextprime(p+1); r = nextprime(q+1); if (isprime(p^2+q^2-r^2), print1(p, ", ")););} \\ _Michel Marcus_, Mar 01 2015
%K A255581 nonn
%O A255581 1,1
%A A255581 _Pierandrea Formusa_, Feb 26 2015