OFFSET
1,2
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..200
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 92
FORMULA
a(n) = n!*A001003(n-1). - Vladeta Jovovic, Dec 06 2002
E.g.f.: series reversion of x*(1-2*x)/(1-x). - Andrew Howroyd, Sep 19 2018
Assuming offset = 0:
a(n) = Sum_{k=0..n} Sum{m=0..k} (-1)^(m + k) * binomial(n + k, n + m) * binomial(n + m - 1, m - 1) * (n + m)! / m!. - Peter Luschny, Sep 26 2022
MATHEMATICA
a[1]=1; a[2]=2; a[n_] := a[n]=3(2n-3)a[n-1]-(n-1)(n-3)a[n-2]
PROG
(PARI) Vec(serlaplace(serreverse(x*(1-2*x)/(1-x) + O(x^20)))) \\ Andrew Howroyd, Sep 19 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Terms a(17) and beyond from Andrew Howroyd, Sep 19 2018
STATUS
approved