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 A035213 #9 Nov 19 2023 01:25:44
%S A035213 1,2,2,3,2,4,0,4,3,4,2,6,0,0,4,5,0,6,0,6,0,4,2,8,3,0,4,0,0,8,1,6,4,0,
%T A035213 0,9,0,0,0,8,2,0,2,6,6,4,0,10,1,6,0,0,0,8,4,0,0,0,0,12,0,2,0,7,0,8,0,
%U A035213 0,4,0,0,12,0,0,6,0,0,0,2,10
%N A035213 Coefficients in expansion of Dirichlet series Product_p (1-(Kronecker(m,p)+1)*p^(-s)+Kronecker(m,p)*p^(-2s))^(-1) for m = 31.
%H A035213 Amiram Eldar, <a href="/A035213/b035213.txt">Table of n, a(n) for n = 1..10000</a>
%F A035213 From _Amiram Eldar_, Nov 19 2023: (Start)
%F A035213 a(n) = Sum_{d|n} Kronecker(31, d).
%F A035213 Multiplicative with a(31^e) = 1, a(p^e) = (1+(-1)^e)/2 if Kronecker(31, p) = -1 (p is in A038906), and a(p^e) = e+1 if Kronecker(31, p) = 1 (p is in A038905 \ {31}).
%F A035213 Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 2*log(273*sqrt(31)+1520)/sqrt(31) = 2.880729917283... . (End)
%t A035213 a[n_] := DivisorSum[n, KroneckerSymbol[31, #] &]; Array[a, 100] (* _Amiram Eldar_, Nov 19 2023 *)
%o A035213 (PARI) my(m = 31); direuler(p=2,101,1/(1-(kronecker(m,p)*(X-X^2))-X))
%o A035213 (PARI) a(n) = sumdiv(n, d, kronecker(31, d)); \\ _Amiram Eldar_, Nov 19 2023
%Y A035213 Cf. A038905, A038906.
%K A035213 nonn,easy,mult
%O A035213 1,2
%A A035213 _N. J. A. Sloane_