OFFSET
0,3
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..410
FORMULA
E.g.f.: (1 - x*cosh(x)) / (1 - 2*x*cosh(x) + x^2).
a(n) = Sum_{k=0..n} n!/k! * ((n-k)^k + (-n+k)^k)/2.
a(n) ~ n! * (1-c*cosh(c)) / (2*(cosh(c)+c*(sinh(c)-1)) * c^(n+1)), where c = A030178 = LambertW(1) = 0.56714329040978387299996866... . - Vaclav Kotesovec, May 21 2015
EXAMPLE
E.g.f.: A(x) = 1 + x + 2*x^2/2! + 9*x^3/3! + 72*x^4/4! + 665*x^5/5! +...
where A(x) = 1 + x*cosh(x) + x^2*cosh(2*x) + x^3*cosh(3*x) + x^4*cosh(4*x) +...
MATHEMATICA
CoefficientList[Series[(1-x*Cosh[x])/(1-2*x*Cosh[x]+x^2), {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, May 21 2015 *)
PROG
(PARI) {a(n) = sum(k=0, n, n!/k! * ((n-k)^k + (-n+k)^k)/2)}
for(n=0, 30, print1(a(n), ", "))
(PARI) {a(n) = local(A=1); A = sum(m=0, n, x^m*cosh(m*x +x*O(x^n))); n!*polcoeff(A, n)}
for(n=0, 30, print1(a(n), ", "))
(PARI) {a(n) = local(X=x+x*O(x^n), A=1); A = (1 - x*cosh(X)) / (1 - 2*x*cosh(X) + x^2); n!*polcoeff(A, n)}
for(n=0, 30, print1(a(n), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, May 20 2015
STATUS
approved