login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A157994 Number of trees with n edges equipped with a cyclic order on their edges, i.e., number of orbits of the action of Z/nZ on the set of edge-labeled trees of size n, given by cyclically permuting the labels. 0
1, 1, 2, 8, 44, 411, 4682, 66524, 1111134, 21437357, 469070942, 11488238992, 311505013052, 9267596377239, 300239975166840, 10523614185609344, 396861212733968144, 16024522976922760209, 689852631578947368422 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..19.

FORMULA

a(1) = 1, a(2) = 1, a(n) = (1/n)*((n+1)^{n-2} + sum_{k=1}^{n-1} (n+1)^{gcd(n,k)-1}) for n > 2

PROG

(Sage) [1, 1] + [((n+1)^(n-2) + sum([(n+1)^(gcd(n, k) -1) for k in [1..n-1]]))/n for n in [3..20]]

CROSSREFS

A007830, A000169

Sequence in context: A336545 A126101 A308478 * A002500 A002833 A348107

Adjacent sequences: A157991 A157992 A157993 * A157995 A157996 A157997

KEYWORD

easy,nonn

AUTHOR

Nikos Apostolakis, Mar 10 2009

EXTENSIONS

Corrected the formula and Sage code - Nikos Apostolakis, Feb 27 2011.

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 4 23:05 EST 2022. Contains 358572 sequences. (Running on oeis4.)