OFFSET
0,3
COMMENTS
See triangle A064334 with columns m built from C(-m; n), m >= 0, also for Derrida et al. references.
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..830
FORMULA
a(n) = Sum_{m=0..n-1} (n-m)*binomial(n-1+m, m)*(-4)^m/n.
a(n) = (1/5)^n*(1 + 4*Sum_{k=0..n-1} C(k)*(-4*5)^k), n >= 1, a(0) = 1; with C(n) = A000108(n) (Catalan).
G.f.: (1+4*x*c(-4*x)/5)/(1-x/5) = 1/(1-x*c(-4*x)) with c(x) g.f. of Catalan numbers A000108.
a(n) = hypergeometric([1-n, n], [-n], -4) for n > 0. - Peter Luschny, Nov 30 2014
MATHEMATICA
CoefficientList[Series[(9 +Sqrt[1+16*x])/(2*(5-x)), {x, 0, 30}], x] (* G. C. Greubel, May 03 2019 *)
PROG
(Sage)
def a(n):
if n==0: return 1
return hypergeometric([1-n, n], [-n], -4).simplify()
[a(n) for n in range(20)] # Peter Luschny, Nov 30 2014
(Sage) ((9 +sqrt(1+16*x))/(2*(5-x))).series(x, 30).coefficients(x, sparse=False) # G. C. Greubel, May 03 2019
(PARI) my(x='x+O('x^30)); Vec((9 +sqrt(1+16*x))/(2*(5-x))) \\ G. C. Greubel, May 03 2019
(Magma) R<x>:=PowerSeriesRing(Rationals(), 30); Coefficients(R!( (9 +Sqrt(1+16*x))/(2*(5-x)) )); // G. C. Greubel, May 03 2019
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Wolfdieter Lang, Sep 21 2001
STATUS
approved