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 A216512 #19 Aug 06 2024 09:34:11
%S A216512 1,0,0,1,0,0,1,1,1,0,1,0,0,0,0,2,0,0,0,0,0,0,1,0,1,0,0,1,1,0,0,2,0,0,
%T A216512 0,1,1,0,0,0,0,0,1,1,0,0,0,0,1,0,0,0,1,0,0,1,0,0,0,0,0,0,1,3,0,0,1,0,
%U A216512 0,0,1,1,0,0,0,0,1,0,1,0,1,0,0,0,0,0,0
%N A216512 Number of nonnegative integer solutions to the equation a^2 + 7*b^2 = n.
%H A216512 Aung Phone Maw, <a href="https://arxiv.org/abs/2408.01763">On the Number of Ways a Natural Number Can Be Written in the Form 7a^2+b^2</a>, arXiv:2408.01763 [math.GM], 2024.
%t A216512 r[n_] := Reduce[x >= 0 && y >= 0 && x^2 + 7 y^2 == n, Integers];
%t A216512 a[n_] := Which[rn = r[n]; rn === False, 0, Head[rn] === And, 1, Head[rn] === Or, Length[rn], True, -1];
%t A216512 Table[a[n], {n, 1, 87}] (* _Jean-François Alcover_, Jun 24 2017 *)
%Y A216512 Cf. A020670.
%K A216512 nonn
%O A216512 1,16
%A A216512 _V. Raman_, Sep 08 2012