OFFSET
0,9
LINKS
R. L. Graham and N. J. A. Sloane, Penny-Packing and Two-Dimensional Codes, Discrete and Comput. Geom. 5 (1990), 1-11.
Craig Knecht, Classification of spaces between the pennies
R. J. Mathar, Illustration of conjectured a(9) to a(24)
Kival Ngaokrajang, Illustration of initial terms
FORMULA
Conjecture (derived from Euler's F+V=E+1 formula): a(n) = 1+(A069813(n)-n)/2 = A001399(n-6), which means g.f. is x^6 / ( (1+x)*(1+x+x^2)*(1-x)^3 ). - R. J. Mathar, Jul 14 2015
EXAMPLE
In the hexagonal lattice packing of pennies, one penny can be enclosed by 6 pennies, 2 pennies by eight pennies, 3 pennies by 9 pennies, 4 pennies by 10 pennies, 5 pennies by 11 pennies, and 7 pennies by 12 pennies.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
N. J. A. Sloane, May 18 2015
EXTENSIONS
a(13) and a(14) from R. J. Mathar, Jul 10 2015
STATUS
approved