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%I #17 Apr 07 2018 03:15:42
%S 1,0,0,0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,
%T 0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
%U 0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
%N G.f.: Sum_{n=-oo..oo} q^(9*n^2 + 2*n).
%H G. C. Greubel, <a href="/A205808/b205808.txt">Table of n, a(n) for n = 0..1000</a>
%H S. Cooper and M. D. Hirschhorn, <a href="http://dx.doi.org/10.1016/S0012-365X(03)00079-7">Results of Hurwitz type for three squares.</a> Discrete Math. 274 (2004), no. 1-3, 9-24. See A(q).
%F Expansion of f(x^7, x^11) in powers of x where f(, ) is Ramanujan's general theta function. - _Michael Somos_, Jan 19 2017
%F Euler transform of a period 36 sequence. - _Michael Somos_, Jan 19 2017
%e G.f. = 1 + x^7 + x^11 + x^32 + x^40 + x^75 + x^87 + x^136 + x^152 + x^215 + ...
%e G.f. = q + q^64 + q^100 + q^289 + q^361 + q^676 + q^784 + q^1225 + q^1369 + ...
%t a[ n_] := SeriesCoefficient[ QPochhammer[ -x^7, x^18] QPochhammer[ -x^11, x^18] QPochhammer[ x^18], {x, 0, n}]; (* _Michael Somos_, Jan 19 2017 *)
%o (PARI) {a(n) = issquare(9*n + 1)}; /* _Michael Somos_, Jan 19 2017 */
%Y Characteristic function of A132355.
%K nonn
%O 0
%A _N. J. A. Sloane_, Jan 31 2012
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