OFFSET
0,5
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..50
FORMULA
E.g.f.: exp(-x+x^2/2)*(Sum_{n>=0} 2^(n*(n-1)/2)*(x/exp(x))^n/n!). - Vladeta Jovovic, Jan 26 2006
Exponential transform of A059166. - Gus Wiseman, Aug 18 2019
Inverse binomial transform of A059167. - Gus Wiseman, Sep 02 2019
EXAMPLE
From Gus Wiseman, Aug 18 2019: (Start)
The a(4) = 10 edge-sets:
{12,13,24,34}
{12,14,23,34}
{13,14,23,24}
{12,13,14,23,24}
{12,13,14,23,34}
{12,13,14,24,34}
{12,13,23,24,34}
{12,14,23,24,34}
{13,14,23,24,34}
{12,13,14,23,24,34}
(End)
MATHEMATICA
m = 13;
egf = Exp[-x + x^2/2]*Sum[2^(n (n-1)/2)*(x/Exp[x])^n/n!, {n, 0, m+1}];
s = egf + O[x]^(m+1);
a[n_] := n!*SeriesCoefficient[s, n];
Table[a[n], {n, 0, m}] (* Jean-François Alcover, Feb 23 2019 *)
Table[Length[Select[Subsets[Subsets[Range[n], {2}]], Union@@#==Range[n]&&Min@@Length/@Split[Sort[Join@@#]]>1&]], {n, 0, 4}] (* Gus Wiseman, Aug 18 2019 *)
PROG
(PARI) seq(n)={Vec(serlaplace(exp(-x + x^2/2 + O(x*x^n))*sum(k=0, n, 2^(k*(k-1)/2)*(x/exp(x + O(x^n)))^k/k!)))} \\ Andrew Howroyd, Sep 04 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Goran Kilibarda, Zoran Maksimovic, Vladeta Jovovic, Jan 03 2005
EXTENSIONS
Terms a(14) and beyond from Andrew Howroyd, Sep 04 2019
STATUS
approved