login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A215985 Number of simple unlabeled graphs on n nodes with exactly 5 connected components that are trees or cycles. 3
1, 1, 3, 6, 13, 26, 55, 112, 238, 510, 1117, 2498, 5712, 13322, 31643, 76455, 187382, 465393, 1168966, 2966298, 7594035, 19597653, 50933434, 133224112, 350477003, 926855665, 2462830565, 6572892862, 17612586165, 47369774428, 127841265076, 346120109957 (list; graph; refs; listen; history; text; internal format)
OFFSET

5,3

LINKS

Alois P. Heinz, Table of n, a(n) for n = 5..650

EXAMPLE

a(7) = 3: .o-o o o.  .o-o o o.  .o o o o.

          .|/     .  .|      .  .| |    .

          .o o o  .  .o o o  .  .o o o  .

MAPLE

with(numtheory):

b:= proc(n) option remember; local d, j; `if`(n<=1, n,

      (add(add(d*b(d), d=divisors(j)) *b(n-j), j=1..n-1))/(n-1))

    end:

g:= proc(n) option remember; local k; `if`(n>2, 1, 0)+ b(n)-

      (add(b(k)*b(n-k), k=0..n) -`if`(irem(n, 2)=0, b(n/2), 0))/2

    end:

p:= proc(n, i, t) option remember; `if`(n<t, 0, `if`(n=t, 1,

      `if`(min(i, t)<1, 0, add(binomial(g(i)+j-1, j)*

       p(n-i*j, i-1, t-j), j=0..min(n/i, t)))))

    end:

a:= n-> p(n, n, 5):

seq(a(n), n=5..40);

CROSSREFS

Column k=5 of A215977.

The labeled version is A215855.

Sequence in context: A320733 A164991 A213255 * A215986 A215987 A215988

Adjacent sequences:  A215982 A215983 A215984 * A215986 A215987 A215988

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Aug 29 2012

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 March 28 15:06 EDT 2020. Contains 333089 sequences. (Running on oeis4.)