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 A215047 #49 Feb 24 2020 00:51:39
%S A215047 3,18,111,840,6655,54109,456361,3954180,34900212,312357933,2826683629,
%T A215047 25814570671,237542444179,2199894223891
%N A215047 Number of primes of the form 1 + b^2 for 1 < b < 10^n.
%C A215047 Primes 1 + b^2 are a form of generalized Fermat primes.
%C A215047 It is conjectured that a(n) is asymptotic to 0.6864067*li(10^n).
%H A215047 Yves Gallot, <a href="http://yves.gallot.pagesperso-orange.fr/primes/results.html">Status of the smallest base values yielding Generalized Fermat primes</a>
%H A215047 Yves Gallot, <a href="http://yves.gallot.pagesperso-orange.fr/primes/stat.html">How many prime numbers appear in a sequence ?</a>
%H A215047 Yves Gallot, <a href="http://yves.gallot.pagesperso-orange.fr/papers/ccdgfpn.html">A Problem on the Conjecture Concerning the Distribution of Generalized Fermat Prime numbers (a new method for the search for large primes)</a>
%H A215047 Mersenne Wiki, <a href="http://mersennewiki.org/index.php/User:Merfighters/listtest">Table of known GF primes b^n+1 where n (exponent) is at least 8192</a>.
%H A215047 Daniel Shanks, <a href="https://doi.org/10.1090/S0025-5718-1960-0120203-6">On the Conjecture of Hardy & Littlewood concerning the Number of Primes of the Form n^2 + a</a>, Math. Comp. 14 (1960), 320-332.
%F A215047 a(n) = A083844(2*n) - 1.
%e A215047 a(1) = 3 because the only generalized Fermat primes F_1(b) where b < 10^1 are the primes: 5, 17, 37.
%t A215047 Table[Length[Select[Range[2,10^n-1]^2 + 1, PrimeQ]], {n, 5}] (* _T. D. Noe_, Aug 02 2012 *)
%o A215047 (PARI) a(n) = sum(b=1,10^n/2-1,isprime((2*b)^2+1))
%Y A215047 Cf. A083844, A206709.
%K A215047 nonn,more
%O A215047 1,1
%A A215047 _Henryk Dabrowski_, Aug 01 2012
%E A215047 a(13)-a(14) from _Jinyuan Wang_, Feb 23 2020