OFFSET
0,2
EXAMPLE
The a(3) = 12 clutters:
{}
{{1}}
{{2}}
{{3}}
{{1,2}}
{{1,3}}
{{2,3}}
{{1,2,3}}
{{1,2},{1,3}}
{{1,2},{2,3}}
{{1,3},{2,3}}
{{1,2},{1,3},{2,3}}
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, May 23 2018
STATUS
approved