OFFSET
0,2
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 0..190
FORMULA
E.g.f. satisfies:
(1) A(x) = exp(2*F(x)) where F(x) = x + F(x)^2*exp(2*F(x)) is the e.g.f. of A214688.
(2) A(x) = Sum_{n>=0} a(n)*x^n/n!, where
a(n) = Sum_{k=0..n} n! * (n-k+1)^(k-1)*2^k/k! * C(2*n-k,n-k)*k/(2*n-k).
(3) Let A(x)^m = Sum_{n>=0} a(n,m)*x^n/n!, then
a(n,m) = Sum_{k=0..n} (m*k*n!/(k!*(2*n-k))) * C(2*n-k,n-k) *(n-k+m)^(k-1)*2^k
...
O.g.f.: A(x) = 1 + Sum_{n>=1} 2*(2*n-2)!/(n-1)! * x^n/(1 - 2*n*x)^(2*n-1).
a(n) ~ n^(n-1) * sqrt((r*s^3*(1-6*r*s+8*r^2*s^2)) / (1 + (1-8*r-2*r^2)*s + 8*r*(-1+2*r+r^2)*s^2 + 4*r^2*(4+r)*s^3)) / (exp(n) * r^n), where s = 1.63431733254223384712742331758... is the root of the equation 1/4*log(s)*(2-s*log(s)) = (-2*s-s^2 + sqrt(2*s+5*s^2+4*s^3+s^4))/(2*s), and r = 1/4*log(s)*(2-s*log(s)) = 0.1470215075962238276175169526... - Vaclav Kotesovec, Feb 26 2014
EXAMPLE
E.g.f.: A(x) = 1 + 2*x + 8*x^2/2! + 80*x^3/3! + 1360*x^4/4! + 32352*x^5/5! +...
log(A(x))/(2*x) = 1 + x*A(x) + 2*x^2*A(x)^2 + 5*x^3*A(x)^3 + 14*x^4*A(x)^4 +...+ A000108(n)*x^n*A(x)^n +...
log(A(x))/2 = x + 2*x^2/2! + 24*x^3/3! + 408*x^4/4! + 9760*x^5/5! +...+ A214688(n)*x^n/n! +...
Ordinary Generating Function:
O.g.f.: 1 + 2*x + 8*x^2 + 80*x^3 + 1360*x^4 + 32352*x^5 + 989824*x^6 +...
O.g.f.: 1 + 2*1*x/(1-2*x) + 2*2*x^2/(1-4*x)^3 + 2*6*2!*x^3/(1-6*x)^5 + 2*20*3!*x^4/(1-8*x)^7 + 2*70*4!*x^5/(1-10*x)^9 + 2*252*5!*x^6/(1-12*x)^11 +...+ 2*(2*n-2)!/(n-1)!*x^n/(1-2*n*x)^(2*n-1) +...
MATHEMATICA
Flatten[{1, Table[Sum[n!*2^k/k!*(n-k+1)^(k-1)*Binomial[2*n-k, n-k] *k/(2*n-k), {k, 0, n}], {n, 1, 20}]}] (* Vaclav Kotesovec, Feb 26 2014 *)
PROG
(PARI) {a(n, m=1)=if(n==0, 1, sum(k=0, n, n!*2^k/k!*m*(m+n-k)^(k-1)*binomial(2*n-k, n-k)*k/(2*n-k)))}
(PARI) {a(n, m=1)=local(A=1+x+x*O(x^n)); for(i=1, n, A=exp(2*(1-sqrt(1-4*x*A))/(2*A))); n!*polcoeff(A^m, n)}
(PARI) /* From o.g.f.: */
{a(n)=polcoeff(1+2*sum(m=1, n, (2*m-2)!/(m-1)!*x^m/(1-2*m*x+x*O(x^n))^(2*m-1)), n)}
for(n=0, 25, print1(a(n), ", "))
(Magma)
A214689:= func< n | n le 1 select n+1 else (&+[k*Binomial(n, k)*Binomial(2*n-k, n-k)*Factorial(n-k)*2^k*(n-k+1)^(k-1)/(2*n-k): k in [0..n]]) >;
[A214689(n): n in [0..30]]; // G. C. Greubel, Mar 07 2024
(SageMath)
def A214689(n): return n+1 if n<2 else sum(k*binomial(n, k)*binomial(2*n-k, n-k)*factorial(n-k)*2^k*(n-k+1)^(k-1)/(2*n-k) for k in range(n+1))
[A214689(n) for n in range(31)] # G. C. Greubel, Mar 07 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Aug 01 2012
STATUS
approved