OFFSET
1,4
COMMENTS
The helm graph H_n is the graph obtained from an n-wheel graph by adjoining a pendant edge at each node of the cycle.
LINKS
J. A. Gallian, A dynamic survey of graph labeling, Elec. J. Combin., (2013), #DS6.
Eric W. Weisstein, Helm Graph
FORMULA
Pi_n(z) = z*((1-z)^n*(z-2)+(z-2)^n*(z-1)^n); a(n) = Pi_n(n).
EXAMPLE
a(3) = 3 * ((1 - 3)^3 * (3 - 2) + (3 - 2)^3 * (3 - 1)^3) = 0.
MAPLE
P := proc(n, z) z*((1-z)^n*(z-2)+(z-2)^n*(z-1)^n) ; end: A147859 := proc(n) P(n, n) ; end: for n from 1 to 15 do printf("%d, ", A147859(n)) ; od: # R. J. Mathar, Jan 22 2009
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Nov 16 2008
EXTENSIONS
Corrected parentheses, definition and values R. J. Mathar, Jan 22 2009
STATUS
approved