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%I #20 Sep 18 2017 18:11:46
%S 1,0,0,0,2,0,12,0,40,10,516,124,5020,1828,48570,32806,527890,444480,
%T 6137942,6482314,70573856,93276044,853480374,1300190254,10660384742,
%U 18371629260,134129890382,259804151324,1728886287134,3667061002286,22672130669968
%N Number of solutions to +- 1^2 +- 3^2 +- 5^2 +- 7^2 +- ... +- (4*n-1)^2 = 0.
%H Seiichi Manyama, <a href="/A292496/b292496.txt">Table of n, a(n) for n = 0..100</a>
%F Constant term in the expansion of Product_{k=1..2*n} (x^(2*k-1)^2+1/x^(2*k-1)^2).
%e For n=4 the 2 solutions are +1^2-3^2-5^2+7^2-9^2+11^2+13^2-15^2 = 0 and -1^2+3^2+5^2-7^2+9^2-11^2-13^2+15^2 = 0.
%o (PARI) a(n) = polcoeff(prod(k=1, 2*n, x^(2*k-1)^2+1/x^(2*k-1)^2), 0); \\ _Michel Marcus_, Sep 18 2017
%Y Cf. A158092, A292476, A292497.
%K nonn
%O 0,5
%A _Seiichi Manyama_, Sep 17 2017