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 A338477 #14 Apr 09 2021 01:04:35 %S A338477 1,3,4,5,6,7,8,9,10,11,13,14,17,18,19,20,22,24,25,27,28,29,33,34,37, %T A338477 38,43,44,46,47,51,52,54,55,58,59,60,67,68,71,73,75,79,80,81,82,83,85, %U A338477 86,87,89,90,93,94,95,96,97,100,103,106,107,108,110,112,114,116,117,119,121,124,125,128 %N A338477 Numbers k such that 398*k^2 - 1 is prime. %C A338477 There are 414 such primes for 1 <= x <= 1000, and 3280 for 1 <= x <= 10000. %H A338477 Robert Israel, <a href="/A338477/b338477.txt">Table of n, a(n) for n = 1..10000</a> %H A338477 V. Granville, <a href="https://mathoverflow.net/questions/375133/quadratic-progressions-with-very-high-prime-density">Quadratic progressions with very high prime density</a>, MathOverflow. %F A338477 a(n) = sqrt(A338476(n) + 1)/398. %e A338477 a(3)=4 is in the sequence because 398*4^2 - 1 = 6367 is prime. %p A338477 select(t -> isprime(398*t^2-1), [$1..1000]); %Y A338477 Cf. A338476. %Y A338477 Cf. A331947, where 398 is a term. %K A338477 nonn %O A338477 1,2 %A A338477 _Robert Israel_, Oct 29 2020