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A370029
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Expansion of g.f. A(x) satisfying Sum_{n=-oo..+oo} (-1)^n * (x^n + 9*A(x))^n = 1 + 11*Sum_{n>=1} (-1)^n * x^(n^2).
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12
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1, 9, 84, 809, 7974, 79863, 809131, 8270199, 85126516, 881290445, 9167900511, 95763822969, 1003839653480, 10554997636854, 111280621221379, 1176017223671139, 12454545436154097, 132149953604522106, 1404591515239624671, 14952277258870348035, 159396459604398283553
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OFFSET
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1,2
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COMMENTS
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A related function is theta_4(x) = 1 + 2*Sum_{n>=1} (-1)^n * x^(n^2).
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LINKS
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FORMULA
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G.f. A(x) = Sum_{n>=1} a(n)*x^n satisfies the following formulas.
(1) Sum_{n=-oo..+oo} (-1)^n * (x^n + 9*A(x))^n = 1 + 11*Sum_{n>=1} (-1)^n * x^(n^2).
(2) Sum_{n=-oo..+oo} (-1)^n * x^n * (x^n + 9*A(x))^(n-1) = 1 + 11*Sum_{n>=1} (-1)^n * x^(n^2).
(3) Sum_{n=-oo..+oo} (-1)^n * x^n * (x^n + 9*A(x))^n = 0.
(4) Sum_{n=-oo..+oo} (-1)^n * x^(n^2) / (1 + 9*A(x)*x^n)^n = 1 + 11*Sum_{n>=1} (-1)^n * x^(n^2).
(5) Sum_{n=-oo..+oo} (-1)^n * x^(n^2) / (1 + 9*A(x)*x^n)^(n+1) = 1 + 11*Sum_{n>=1} (-1)^n * x^(n^2).
(6) Sum_{n=-oo..+oo} (-1)^n * x^(n*(n+1)) / (1 + 9*A(x)*x^n)^(n+1) = 0.
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EXAMPLE
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G.f.: A(x) = x + 9*x^2 + 84*x^3 + 809*x^4 + 7974*x^5 + 79863*x^6 + 809131*x^7 + 8270199*x^8 + 85126516*x^9 + 881290445*x^10 + 9167900511*x^11 + 95763822969*x^12 + ...
where
Sum_{n=-oo..+oo} (-1)^n * (x^n + 9*A(x))^n = 1 - 11*x + 11*x^4 - 11*x^9 + 11*x^16 - 11*x^25 + 11*x^36 - 11*x^49 +- ...
SPECIAL VALUES.
(V.1) Let A = A(exp(-Pi)) = 0.07175219834164736620386280600888962717215573957821859403...
then Sum_{n=-oo..+oo} (-1)^n * (exp(-n*Pi) + 9*A)^n = (11*(Pi/2)^(1/4)/gamma(3/4) - 9)/2 = 0.5246852598586425177...
(V.2) Let A = A(exp(-2*Pi)) = 0.001899385878782719362352219788087550672661478114904760835...
then Sum_{n=-oo..+oo} (-1)^n * (exp(-2*n*Pi) + 9*A)^n = (11*2^(1/8)*(Pi/2)^(1/4)/gamma(3/4) - 9)/2 = 0.97945813008498924684...
(V.3) Let A = A(-exp(-Pi)) = -0.03120408533767785789845054540220571847531668789278074466...
then Sum_{n=-oo..+oo} (-1)^n * ((-1)^n*exp(-n*Pi) + 9*A)^n = (11*Pi^(1/4)/gamma(3/4) - 9)/2 = 1.475391461673194080164...
(V.4) Let A = A(-exp(-2*Pi)) = -0.001836594032195533189068390983153367342311468510211476381...
then Sum_{n=-oo..+oo} (-1)^n * ((-1)^n*exp(-2*n*Pi) + 9*A)^n = (11*sqrt(2 + sqrt(2))/2 * Pi^(1/4)/gamma(3/4) - 9)/2 = 1.0205418701825650...
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PROG
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(PARI) {a(n) = my(A=[0, 1]); for(i=1, n, A = concat(A, 0);
A[#A] = polcoeff( sum(m=-#A, #A, (-1)^m * (x^m + 9*Ser(A))^m ) - 1 - 11*sum(m=1, #A, (-1)^m * x^(m^2) ), #A-1)/9 ); A[n+1]}
for(n=1, 30, print1(a(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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