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A193235
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G.f.: A(x) = ( Sum_{n>=0} (-4)^n * x^(n^2) )^(-1/2).
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1
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1, 2, 6, 20, 62, 204, 684, 2312, 7926, 27436, 95572, 334872, 1178796, 4164984, 14763096, 52471056, 186928422, 667295052, 2386388356, 8547855032, 30661465476, 110125076328, 395989755496, 1425411710064, 5135888179644, 18521445768696, 66847890766152
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OFFSET
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0,2
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LINKS
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EXAMPLE
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G.f.: A(x) = 1 + 2*x + 6*x^2 + 20*x^3 + 62*x^4 + 204*x^5 + 684*x^6 +...
where
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) +...
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PROG
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(PARI) {a(n)=local(S=sum(m=0, sqrtint(n), (-4)^m*x^(m^2))+x*O(x^n)); polcoeff(S^(-1/2), n)}
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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