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Expansion of g.f. A(x) satisfying A(x)^5 = A( x^5/(1 - 5*x)^5 ) / (1 - 5*x).
3

%I #11 Mar 25 2023 13:20:05

%S 1,1,3,11,44,185,806,3627,16926,82615,425633,2325804,13438568,

%T 81258283,507109592,3223435416,20655599675,132496854084,847152571284,

%U 5386490329194,34026141582719,213512516149309,1331393810596499,8255968489237781,50955585198416275,313329163267012645

%N Expansion of g.f. A(x) satisfying A(x)^5 = A( x^5/(1 - 5*x)^5 ) / (1 - 5*x).

%C Related Catalan identity: C(x)^2 = C( x^2/(1 - 2*x)^2 ) / (1 - 2*x), where C(x) = 1 + x*C(x)^2 is the g.f. of the Catalan numbers (A000108).

%C Radius of convergence of g.f. A(x) is r where r is the real root of r = (1 - 5*r)^(5/4) with A(r) = 1/r^(1/5) = 1.451902871451714... so that A(r)^5 = A(r)/(1 - 5*r) and r = 0.1549930338264677513709380922535...

%H Paul D. Hanna, <a href="/A361764/b361764.txt">Table of n, a(n) for n = 0..500</a>

%F G.f. A(x) = Sum_{n>=0} a(n)*x^n satisfies:

%F (1) A(x)^5 = A( x^5/(1 - 5*x)^5 ) / (1 - 5*x).

%F (2) A(x^5) = A( x/(1 + 5*x) )^5 / (1 + 5*x).

%F (3) A(x) = Product_{n>=1} 1/(1 - 5/F(n,x))^(1/5^n), where F(1,x) = 1/x, F(m,x) = (F(m-1,x) - 5)^5 for m > 1.

%e G.f.: A(x) = 1 + x + 3*x^2 + 11*x^3 + 44*x^4 + 185*x^5 + 806*x^6 + 3627*x^7 + 16926*x^8 + 82615*x^9 + 425633*x^10 + ...

%e such that A(x)^5 = A( x^5/(1 - 5*x)^5 ) / (1 - 5*x).

%e RELATED SERIES.

%e A(x)^5 = 1 + 5*x + 25*x^2 + 125*x^3 + 625*x^4 + 3126*x^5 + 15655*x^6 + 78650*x^7 + 397625*x^8 + 2031875*x^9 + 10553128*x^10 + ...

%e A( x^5/(1 - 5*x)^5 ) = 1 + x^5 + 25*x^6 + 375*x^7 + 4375*x^8 + 43750*x^9 + 393753*x^10 + 3281400*x^11 + 25785375*x^12 + ...

%e SPECIFIC VALUES.

%e A(1/7) = ( 7/2 * A(1/32) )^(1/5) = 1.293495906485927953020670787280...

%e A(1/7) = (1 - 5/7)^(-1/5) * (1 - 5/32)^(-1/25) * (1 - 5/14348907)^(-1/125) * (1 - 5/14348902^5)^(-1/625) * ...

%e A(1/8) = ( 8/3 * A(1/243) )^(1/5) = 1.21774097368643014934892826038499995...

%e A(1/8) = (1 - 5/8)^(-1/5) * (1 - 5/243)^(-1/25) * (1 - 5/763633171168)^(-1/125) * (1 - 5/763633171163^5)^(-1/625) * ...

%e A(1/10) = ( 2 * A(1/3125) )^(1/5) = 1.14877193292427434012390599513357372...

%e A(1/10) = (1 - 5/10)^(-1/5) * (1 - 5/3125)^(-1/25) * (1 - 5/295646655283200000)^(-1/125) * (1 - 5/295646655283199995^5)^(-1/625) * ...

%o (PARI) {a(n) = my(A=1); for(i=1, #binary(n+1), A = ( subst(A, x, x^5/(1 - 5*x +x*O(x^n))^5 )/(1 - 5*x +x*O(x^n)) )^(1/5) ); polcoeff(A, n)}

%o for(n=0, 30, print1(a(n), ", "))

%Y Cf. A361765, A361762, A091200, A000108.

%K nonn

%O 0,3

%A _Paul D. Hanna_, Mar 24 2023