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A243013
Number of graphs with n vertices and n-1 edges that can be gracefully labeled.
0
1, 1, 1, 3, 5, 12, 36
OFFSET
1,4
COMMENTS
Hand calculated by grade 3 students up to term 6: (1,1,1,3,5,12...)
EXAMPLE
a(5) = 5: A001433 tells us that there are 6 simple graphs with 5 vertices and 4 edges. Only 5 of these can be labeled gracefully. The one that cannot is the triangular loop plus two connected nodes: ∆ / .
CROSSREFS
A001433 provides an upper bound. If the Graceful Tree Conjecture were true, A000055 would be a lower bound.
Sequence in context: A323270 A376161 A087610 * A191636 A267337 A308544
KEYWORD
more,nonn
AUTHOR
Gordon Hamilton, May 28 2014
STATUS
approved