cp's OEIS Frontend

A169783 Number of solutions to a^2 + b^2 + 4*c^2 = n.

%I A169783 #6 Aug 01 2018 10:30:00
%S A169783 1,4,4,0,6,16,8,0,12,20,8,0,8,16,16,0,6,32,12,0,24,32,8,0,24,20,24,0,
%T A169783 0,48,16,0,12,32,16,0,30,16,24,0,24,64,16,0,24,48,16,0,8,36,28,0,24,
%U A169783 48,32,0,48,32,8,0,0,48,32,0,6,64,32,0,48,64,16,0,36,32,40,0,24,64,16,0,24,68
%N A169783 Number of solutions to a^2 + b^2 + 4*c^2 = n.
%F A169783 G.f.: theta_3(q)^2*theta_3(q^4), where theta_3() is the Jacobi theta function. - _Ilya Gutkovskiy_, Aug 01 2018
%p A169783 t0:=Array(0..10000,0); M:=15;
%p A169783 for i from -M to M do for j from -M to M do for k from -M to M do
%p A169783 t1:=i^2+j^2+4*k^2; t0[t1]:=t0[t1]+1; od: od: od:
%p A169783 [seq(t0[i],i=0..100)];
%Y A169783 x^2+y^2+k*z^2: A005875, A014455, A034933, A169784.
%K A169783 nonn
%O A169783 0,2
%A A169783 _N. J. A. Sloane_, May 12 2010