OFFSET
1,2
LINKS
Gheorghe Coserea, Table of n, a(n) for n = 1..200
Michael Borinsky, Generating asymptotics for factorially divergent sequences, arXiv preprint arXiv:1603.01236 [math.CO], 2016. See M_n.
FORMULA
G.f.: C(x/(1-x)^2), where C(x) is the g.f. for A000699.
MATHEMATICA
terms = 20;
c[_] = 0;
Do[c[x_] = x + x^2*D[c[x]^2/x, x] + O[x]^(terms+1) // Normal, terms];
c[x/(1-x)^2] + O[x]^(terms+1) // CoefficientList[#, x]& // Rest (* Jean-François Alcover, Sep 01 2018 *)
PROG
(PARI)
A000699_seq(N) = {
my(a = vector(N)); a[1] = 1;
for (n=2, N, a[n] = sum(k=1, n-1, (2*k-1)*a[k]*a[n-k])); a;
};
N = 20; Vec(subst(x*Ser(A000699_seq(N)), x, x/(1-x)^2)) \\ Gheorghe Coserea, Jan 22 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jan 19 2017
STATUS
approved