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A295538
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G.f. A(x) satisfies A(x)^2 = 1 + x + x*A(x)^9.
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6
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1, 1, 4, 32, 290, 2894, 30624, 337602, 3835395, 44588657, 527903344, 6343105788, 77153875396, 948150877136, 11754481411170, 146829606548967, 1846232392749705, 23349436820785896, 296822925777158448, 3790612373731979898, 48608130217245939310, 625636961746371994680, 8079794260209350950338, 104667769434155291997329, 1359712949654853908780859, 17709395639599543591065564
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OFFSET
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0,3
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COMMENTS
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Note that the function G(x) = 1 + x*G(x)^4 (g.f. of A002293) also satisfies the condition: G(x) = 1/G(-x*G(x)^7).
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LINKS
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FORMULA
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G.f. A(x) satisfies:
(1) A(x) = 1 + Series_Reversion( x/(1 + 4*x + 16*x^2 + 34*x^3 + 46*x^4 + 40*x^5 + 22*x^6 + 7*x^7 + x^8) ).
(2) F(A(x)) = x such that F(x) = -(1 - x^2)/(1 + x^9).
(3) A(x) = 1 / A(-x*A(x)^7).
a(n) ~ sqrt((1 + s^9)/(7*Pi)) / (2*n^(3/2)*r^(n - 1/2)), where r = 0.07223758934231429961770532152600550503126361567079... and s = 1.174134228398636389214738979941451774138268651734... are real roots of the system of equations 1 + r + r*s^9 = s^2, 9*r*s^7 = 2. - Vaclav Kotesovec, Nov 28 2017
G.f. A(x) satisfies A(x) = 1 + x * (1 - A(x) + A(x)^2 - A(x)^3 + A(x)^4 - A(x)^5 + A(x)^6 - A(x)^7 + A(x)^8).
a(n) = Sum_{k=0..n} binomial(n,k) * binomial(9*k/2+1/2,n)/(9*k+1). (End)
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EXAMPLE
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G.f.: A(x) = 1 + x + 4*x^2 + 32*x^3 + 290*x^4 + 2894*x^5 + 30624*x^6 + 337602*x^7 + 3835395*x^8 + 44588657*x^9 + 527903344*x^10 + 6343105788*x^11 + 77153875396*x^12 + 948150877136*x^13 + 11754481411170*x^14 + 146829606548967*x^15 +...
such that A(x)^2 = 1+x + x*A(x)^9.
RELATED SERIES.
A(x)^2 = 1 + 2*x + 9*x^2 + 72*x^3 + 660*x^4 + 6624*x^5 + 70380*x^6 + 778164*x^7 + 8860302*x^8 + 103187376*x^9 + 1223410846*x^10 +...
A(x)^9 = 1 + 9*x + 72*x^2 + 660*x^3 + 6624*x^4 + 70380*x^5 + 778164*x^6 + 8860302*x^7 + 103187376*x^8 + 1223410846*x^9 + 14717253672*x^10 +...
A(-x*A(x)^7) = 1 - x - 3*x^2 - 25*x^3 - 221*x^4 - 2187*x^5 - 22989*x^6 - 252237*x^7 - 2855304*x^8 - 33101152*x^9 - 391010608*x^10 +...
which equals 1/A(x).
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PROG
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(PARI) {a(n) = my(A=1+x); for(i=1, n, A = sqrt(1+x + x*A^9 +x*O(x^n)) ); polcoeff(A, n)}
for(n=0, 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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