OFFSET
0,3
LINKS
Harvey P. Dale, Table of n, a(n) for n = 0..380
Vladimir Kruchinin, D. V. Kruchinin, Composita and their properties , arXiv:1103.2582 [math.CO], 2011-2013.
FORMULA
E.g.f.: exp((1 - x - sqrt(1 - 2*x - 3*x^2))/(2x)).
a(n) = (n-1)!*Sum_{k=1..n} (1/(k-1)!)*Sum_{j=ceiling((n+k)/2)..n} binomial(n,j)*binomial(j,2*j-n-k). - Vladimir Kruchinin, Aug 11 2010
a(n) ~ 3^(n+1/2)*n^(n-1)/(sqrt(2)*exp(n-1)). - Vaclav Kotesovec, Oct 05 2013
Conjecture D-finite with recurrence: +(-2*n+3)*a(n) +(-2*n^3+9*n^2-9*n+1)*a(n-1) +(n-1)*(n-2)*(4*n^2-2*n-3)*a(n-2) +3*(n-1)*(n-3)*(2*n-1)*(n-2)^2*a(n-3)=0. - R. J. Mathar, Jan 24 2020
MATHEMATICA
#/Sqrt[E]&/@With[{nn=20}, CoefficientList[Series[Exp[(1-Sqrt[1-2x-3x^2])/ (2x)], {x, 0, nn}], x]Range[0, nn]!] (* Harvey P. Dale, Oct 26 2011 *)
CROSSREFS
KEYWORD
easy,nice,nonn
AUTHOR
Emanuele Munarini, Mar 31 2003
STATUS
approved