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 A331947 #11 Feb 21 2020 10:59:47
%S A331947 2,12,20,68,90,98,132,252,318,362,398,1722,259668,315180,452042
%N A331947 Factors k > 1 such that the polynomial k*x^2 - 1 produces a record of its Hardy-Littlewood constant.
%C A331947 a(16) > 710000.
%C A331947 See A331940 for more information on the Hardy-Littlewood constant. The polynomials described by this sequence have an increasing rate of generating primes.
%C A331947 The following table provides the record values of the Hardy-Littlewood constant C, together with the number of primes np generated by the polynomial P(x) = a(n)*x^2 - 1 for 2 <= x <= r = 10^8 and the actual ratio np*(P(r)/r)/Integral_{x=2..P(r)} 1/log(x) dx.
%C A331947 a(n) C np C from ratio
%C A331947 2 3.70011 10448345 3.81422
%C A331947 12 4.15027 11154934 4.27219
%C A331947 20 4.43326 11753085 4.56136
%C A331947 68 5.01601 12883801 5.15797
%C A331947 .. ....... ........ .......
%C A331947 315180 7.82318 16502584 8.00057
%C A331947 452042 7.85323 16434699 8.02696
%D A331947 Henri Cohen, Number Theory, Volume II: Analytic and Modern Tools, GTM Vol. 240, Springer, 2007; see pp. 208-209.
%H A331947 Karim Belabas, Henri Cohen, <a href="/A221712/a221712.gp.txt">Computation of the Hardy-Littlewood constant for quadratic polynomials</a>, PARI/GP script, 2020.
%H A331947 Henri Cohen, <a href="/A221712/a221712.pdf">High precision computation of Hardy-Littlewood constants</a>, preprint, 1998. [pdf copy, with permission]
%Y A331947 Cf. A221712, A331940, A331941, A331945, A331946, A331948, A331949.
%K A331947 nonn,more,hard
%O A331947 1,1
%A A331947 _Hugo Pfoertner_, Feb 10 2020