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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
LINKS
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
Sequence in context: A226679 A216541 A347896 * A294385 A020099 A182392
KEYWORD
nonn,hard,more
AUTHOR
Don Knuth, Aug 15 2011
STATUS
approved

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Last modified July 13 01:42 EDT 2024. Contains 374259 sequences. (Running on oeis4.)