OFFSET
1,3
LINKS
Paul D. Hanna, Table of n, a(n) for n = 1..301
FORMULA
G.f. A(x) = Sum_{n>=1} a(n)*x^n satisfies the following formulas.
(1) A(x) = Sum_{n>=0} x^(n+1) * Product_{k=0..n} (x^k + A(x)).
(2) A(x) = -1 + Sum_{n>=1} x^(n*(n-1)/2) / Product_{k=1..n} (1 - x^k*A(x)).
(3) A(x) = x*(1 + A(x))/(1 + F(1)), where F(n) = -x*(x^n + A(x))/(1 + x*(x^n + A(x)) + F(n+1)), a continued fraction.
a(n) ~ c * d^n / n^(3/2), where d = 3.218593300531637233032114... and c = 0.551420536503431682402569... - Vaclav Kotesovec, Feb 19 2024
EXAMPLE
G.f.: A(x) = x + x^2 + 3*x^3 + 6*x^4 + 14*x^5 + 37*x^6 + 95*x^7 + 253*x^8 + 692*x^9 + 1918*x^10 + 5389*x^11 + 15316*x^12 + ...
where A = A(x) satisfies the following sums
(1) A(x) = x*(1 + A) + x^2*(1 + A)*(x + A) + x^3*(1 + A)*(x + A)*(x^2 + A) + x^4*(1 + A)*(x + A)*(x^2 + A)*(x^3 + A) + x^5*(1 + A)*(x + A)*(x^2 + A)*(x^3 + A)*(x^4 + A) + ...
and
(2) A(x) = -1 + 1/(1 - x*A) + x/((1 - x*A)*(1 - x^2*A)) + x^3/((1 - x*A)*(1 - x^2*A)*(1 - x^3*A)) + x^6/((1 - x*A)*(1 - x^2*A)*(1 - x^3*A)*(1 - x^4*A)) + x^10/((1 - x*A)*(1 - x^2*A)*(1 - x^3*A)*(1 - x^4*A)*(1 - x^5*A)) + ...
Further, A = A(x) satisfies the continued fraction
(3) A(x) = x*(1 + A)/(1 - x*(x + A)/(1 + x*(x + A) - x*(x^2 + A)/(1 + x*(x^2 + A) - x*(x^3 + A)/(1 + x*(x^3 + A) - x*(x^4 + A)/(1 + x*(x^4 + A) - x*(x^5 + A)/(1 + x*(x^5 + A) - x*(x^6 + A)/(1 + x*(x^6 + A) + ...))))))).
SPECIFIC VALUES.
A(1/5) = 0.2831219305595313547666016802108274164605432946401360...
A(1/4) = 0.4243087446597560528411347345223789877598412481770880...
A(2/7) = 0.6005081784072201810613576293832454565671753437307175...
A(3/10) = 0.7311141939170660477367006904610649127841162783569496...
A(t) = 0.8 at t = 0.30467385134189076808464770503464780231936925568...
A(t) = 0.9 at t = 0.30882465867699125967932563981416443155628939160...
A(t) = 1 at t = 0.3105475527580721794415140688271783377114855761284799179...
A(x) at x = 1/3 diverges.
PROG
(PARI) {a(n) = my(A=[1]); for(i=1, n, A = Vec( sum(m=0, #A, x^(m+1) * prod(k=0, m, x^k + x*Ser(A)) ) ) ); A[n]}
for(n=1, 40, print1(a(n), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Feb 05 2024
STATUS
approved