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 A343121 #20 Aug 28 2022 04:28:36 %S A343121 2,2,2,2,2,2669,34559,26507494,3242781025 %N A343121 a(n) is the least A for which there exists B with 0 < B < A so that A^(2^k) + B^(2^k) is prime for k = 0, 1, ..., n. %C A343121 For n < 5, the corresponding primes are Fermat primes, for higher n so-called generalized Fermat primes. %H A343121 Yves Gallot, <a href="https://github.com/galloty/GFP/tree/master/xgfp8">xgfp8</a>, software for calculating this sequence. %e A343121 For n=5, the six numbers 2669 + 720, 2669^2 + 720^2, 2669^4 + 720^4, 2669^8 + 720^8, 2669^16 + 720^16, and 2669^32 + 720^32 are all prime, and (A,B) = (2669,720) is the least pair with this property, so a(5)=2669. %e A343121 For n=6, (A,B) = (34559,29000). %e A343121 For n=7, (A,B) = (26507494,6329559). %e A343121 For n=8, (A,B) = (3242781025,1554825312). %o A343121 (PARI) a(n)=for(A=1, oo, for(B=1, A-1, for(k=0, n, !ispseudoprime(A^(2^k)+B^(2^k)) && next(2)); return(A))) %Y A343121 Cf. A090872, A111635, A291944, A343120. %K A343121 nonn,more,hard %O A343121 0,1 %A A343121 _Jeppe Stig Nielsen_, Apr 05 2021 %E A343121 a(7) from _Kellen Shenton_, May 28 2022 %E A343121 a(8) from _Kellen Shenton_, Aug 27 2022