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 A306503 #11 Mar 31 2019 04:03:24
%S A306503 23338590792,2946,1,2,3,1,5,2,1,3,1,5,1,5,16,1,6,7,1,2,3,38,2,1,1,5,3,
%T A306503 1,11,11,1,1,2,9,1,13,2,1,6,15,1,3,8,4,5,1,43,1,2,8,1,1760,2,1,10,3,1,
%U A306503 13,29,1,5,1,11,17,2,1,8,1,5,16,1,171,33,1,4,1,2,3
%N A306503 a(n) is the index in primes of A306500(n), or 0 if A306500(n) = 0.
%C A306503 a(n) is the smallest integer k such that Sum_{i=1..k} Kronecker(-A003657(n),prime(i)) > 0, or 0 if no such k exists.
%C A306503 See A306500 for the actual primes.
%e A306503 See A306500 for the example that shows a(18) = 7.
%o A306503 (PARI) b(n) = my(i=0); forprime(p=2, oo, i+=kronecker(n, p); if(i>0, return(p)))
%o A306503 print1(23338590792, ", "); for(n=4, 300, if(isfundamental(-n), print1(primepi(b(-n)), ", ")))
%Y A306503 Cf. A003657, A306500, A306502.
%K A306503 nonn
%O A306503 1,1
%A A306503 _Jianing Song_, Feb 19 2019