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%I #7 Mar 30 2012 18:37:28
%S 1,2,6,20,62,204,684,2312,7926,27436,95572,334872,1178796,4164984,
%T 14763096,52471056,186928422,667295052,2386388356,8547855032,
%U 30661465476,110125076328,395989755496,1425411710064,5135888179644,18521445768696,66847890766152
%N G.f.: A(x) = ( Sum_{n>=0} (-4)^n * x^(n^2) )^(-1/2).
%e G.f.: A(x) = 1 + 2*x + 6*x^2 + 20*x^3 + 62*x^4 + 204*x^5 + 684*x^6 +...
%e where
%e 1/A(x)^2 = 1 - 4*x + 16*x^4 - 64*x^9 + 256*x^16 - 1024*x^25 + 4096*x^36 - 16384*x^49 +...+ (-4)^n*x^(n^2) +...
%o (PARI) {a(n)=local(S=sum(m=0,sqrtint(n),(-4)^m*x^(m^2))+x*O(x^n));polcoeff(S^(-1/2),n)}
%Y Cf. A193234.
%K nonn
%O 0,2
%A _Paul D. Hanna_, Jul 18 2011
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