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A194090 The number of biconnected squaregraphs of perimeter 2*n. 5
1, 1, 1, 3, 8, 35, 172, 1121, 8017, 63213 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

The CWEB program squaregraph.w cited below relates a(n) to the number of certain partitions of {1,2,...,2*n} into n pairs.

REFERENCES

See A194088

LINKS

Table of n, a(n) for n=1..10.

Don Knuth, squaregraph.w (CWEB program).

EXAMPLE

For n=4 the a(4)=3 cases of perimeter 8 are the two trominoes and the square tetromino.

PROG

(CWEB) (see Knuth link).

CROSSREFS

A194088, A194089, A194091, A194092, A194093.

Sequence in context: A304726 A226679 A216541 * A294385 A020099 A182392

Adjacent sequences:  A194087 A194088 A194089 * A194091 A194092 A194093

KEYWORD

nonn,hard,more

AUTHOR

Don Knuth, Aug 15 2011

STATUS

approved

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Last modified August 1 02:49 EDT 2021. Contains 346379 sequences. (Running on oeis4.)