login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A293510 Number of connected minimal covers of n vertices. 20
1, 1, 1, 4, 23, 241, 3732, 83987, 2666729, 117807298, 7217946453, 612089089261, 71991021616582, 11761139981560581, 2675674695560997301, 849270038176762472316, 376910699272413914514283, 234289022942841270608166061, 204344856617470777364053906796 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

A cover of a finite set S is a finite set of finite nonempty sets with union S. A cover is minimal if removing any edge results in a cover of strictly fewer vertices. A cover is connected if it is connected as a hypergraph or clutter. Note that minimality is with respect to covering rather than to connectedness (cf. A030019).

LINKS

Table of n, a(n) for n=0..18.

EXAMPLE

The a(3) = 4 covers are: ((12)(13)), ((12)(23)), ((13)(23)), ((123)).

MATHEMATICA

nn=30; ser=Sum[(1+Sum[Binomial[n, i]*StirlingS2[i, k]*(2^k-k-1)^(n-i), {k, 2, n}, {i, k, n}])*x^n/n!, {n, 0, nn}];

Table[n!*SeriesCoefficient[1+Log[ser], {x, 0, n}], {n, 0, nn}]

CROSSREFS

Cf. A030019, A046165, A048143, A275307, A283877.

Sequence in context: A316083 A326501 A123637 * A234595 A327367 A303652

Adjacent sequences:  A293507 A293508 A293509 * A293511 A293512 A293513

KEYWORD

nonn

AUTHOR

Gus Wiseman, Oct 11 2017

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 12 07:00 EST 2019. Contains 329948 sequences. (Running on oeis4.)