%I #15 Jun 24 2017 12:11:45
%S 1,1,0,0,1,0,1,1,0,1,1,0,0,0,0,1,1,0,0,0,0,0,1,0,1,2,0,0,1,0,0,1,0,1,
%T 0,0,1,0,0,0,1,0,1,0,0,0,0,0,0,2,0,0,0,0,1,2,0,0,1,0,1,0,0,1,1,0,0,0,
%U 0,0,2,0,0,1,0,0,0,0,0,1,0,1,0,0,0,0,0,1,1,0,1,0,0,0,0,0,1,1,0,0
%N Number of nonnegative integer solutions to the equation x^2 + 6*y^2 = n.
%t r[n_] := Reduce[x >= 0 && y >= 0 && x^2 + 6 y^2 == n, Integers];
%t a[n_] := Which[rn = r[n]; rn === False, 0, Head[rn] === And, 1, Head[rn] === Or, Length[rn], True, -1];
%t Table[a[n], {n, 0, 99}] (* _Jean-François Alcover_, Jun 24 2017 *)
%Y Cf. A002481.
%K nonn
%O 0,26
%A _V. Raman_, Sep 08 2012
%E Verified by _N. J. A. Sloane_, Sep 10 2012
%E a(96) and a(97) corrected by _Jean-François Alcover_, Jun 24 2017