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 A325071 #15 Apr 12 2019 08:25:13 %S A325071 101,181,401,461,521,541,761,941,1021,1061,1361,1601,1621,1721,1741, %T A325071 1861,2081,2441,2621,2801,2861,3001,3121,3301,3461,3581,3821,3881, %U A325071 4001,4021,4201,4441,4561,4621,4861,5021,5081,5101,5261,5281,5441,5741,5861,5981,6221 %N A325071 Prime numbers congruent to 1 modulo 20 representable by both x^2 + 20*y^2 and x^2 + 100*y^2. %C A325071 Brink showed that prime numbers congruent to 1 modulo 20 are representable by both or neither of the quadratic forms x^2 + 20*y^2 and x^2 + 100*y^2. This sequence corresponds to those representable by both, and A325072 corresponds to those representable by neither. %H A325071 David Brink, <a href="https://doi.org/10.1016/j.jnt.2008.04.007">Five peculiar theorems on simultaneous representation of primes by quadratic forms</a>, Journal of Number Theory 129(2) (2009), 464-468, doi:10.1016/j.jnt.2008.04.007, MR 2473893. %H A325071 Rémy Sigrist, <a href="/A325071/a325071.gp.txt">PARI program for A325071</a> %H A325071 Wikipedia, <a href="https://en.wikipedia.org/wiki/Kaplansky%27s_theorem_on_quadratic_forms">Kaplansky's theorem on quadratic forms</a> %e A325071 Regarding 1601: %e A325071 - 1601 is a prime number, %e A325071 - 1601 = 80*20 + 1, %e A325071 - 1601 = 39^2 + 20*2^2 = 1^2 + 100*4^2, %e A325071 - hence 1601 belongs to this sequence. %o A325071 (PARI) See Links section. %Y A325071 See A325067 for similar results. %Y A325071 Cf. A141881, A325072. %K A325071 nonn %O A325071 1,1 %A A325071 _Rémy Sigrist_, Mar 27 2019