OFFSET
0,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..200
EXAMPLE
The a(3) = 8 hypertrees:
{}
{{1,2}}
{{1,3}}
{{2,3}}
{{1,2,3}}
{{1,2},{1,3}}
{{1,2},{2,3}}
{{1,3},{2,3}}
PROG
(PARI) \\ here b(n) is A030019 with b(1)=0.
b(n)=if(n<2, n==0, sum(i=0, n, stirling(n-1, i, 2)*n^(i-1)));
a(n)=sum(k=0, n, binomial(n, k)*b(k)); \\ Andrew Howroyd, Aug 27 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, May 23 2018
STATUS
approved