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 A204993 #28 May 16 2024 20:35:34
%S A204993 4,8,3,4,20,24,7,8,4,40,11,3,52,56,15,4,68,8,19,20,84,88,23,24,4,104,
%T A204993 3,7,116,120,31,8,132,136,35,4,148,152,39,40,164,168,43,11,20,184,47,
%U A204993 3,4,8,51,52,212,24,55,56,228,232,59,15,244,248,7,4,260
%N A204993 Negative of the discriminant of quadratic field Q(sqrt(-n)).
%C A204993 For the discriminant of the quadratic field Q(sqrt(n)), see A037449.
%C A204993 a(n) is the smallest positive N such that ((-n)/k) = ((-n)/(k mod N)) for every odd k that is coprime to n, where ((-n)/k) is the Jacobi symbol. As we have Dirichlet's theorem on arithmetic progressions, a(n) is also the smallest positive N such that ((-n)/p) = ((-n)/(p mod N)) for every odd prime p that is not a factor of n. - _Jianing Song_, May 16 2024
%F A204993 Let b(n) = A007913(n), then a(n) = b(n) if b(n) == 3 (mod 4) and 4*b(n) otherwise. - _Jianing Song_, May 16 2024
%t A204993 -Table[NumberFieldDiscriminant[Sqrt[-n]], {n, 1, 70}]
%o A204993 (PARI) a(n) = -quaddisc(-n) \\ _Jianing Song_, May 16 2024
%Y A204993 Cf. A037449, A007913.
%K A204993 nonn,easy
%O A204993 1,1
%A A204993 _Artur Jasinski_, Jan 27 2012