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!)
A122087 Triangle read by rows: T(n,k) = number of unlabeled free bicolored trees with n nodes (n >= 1) and k (1 <= k <= floor(n/2), except k = 0 if n = 1 ) nodes of one color and n-k nodes of the other color (the colors are interchangeable). 1
1, 1, 1, 1, 1, 1, 2, 1, 2, 3, 1, 3, 7, 1, 3, 10, 9, 1, 4, 14, 28, 1, 4, 19, 45, 37, 1, 5, 24, 73, 132, 1, 5, 30, 105, 242, 168, 1, 6, 37, 152, 412, 693, 1, 6, 44, 204, 660, 1349, 895, 1, 7, 52, 274, 1008, 2472, 3927, 1, 7, 61, 351, 1479, 4219, 8105, 5097, 1, 8 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,7

REFERENCES

R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1978.

LINKS

R. W. Robinson, Rows 1 through 30, flattened

EXAMPLE

K M N gives the number N of unlabeled free bicolored trees with K nodes of one color and M nodes of the other color.

0 1 1

Total( 1) = 1

1 1 1

Total( 2) = 1

1 2 1

Total( 3) = 1

1 3 1

2 2 1

Total( 4) = 2

1 4 1

2 3 2

Total( 5) = 3

1 5 1

2 4 2

3 3 3

Total( 6) = 6

1 6 1

2 5 3

3 4 7

Total( 7) = 11

1 7 1

2 6 3

3 5 10

4 4 9

Total( 8) = 23

CROSSREFS

Row sums give A000055.

Sequence in context: A144215 A254539 A283827 * A139642 A264744 A143604

Adjacent sequences:  A122084 A122085 A122086 * A122088 A122089 A122090

KEYWORD

nonn,tabf

AUTHOR

N. J. A. Sloane, Oct 19 2006

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 May 17 12:01 EDT 2021. Contains 343971 sequences. (Running on oeis4.)