OFFSET
0,2
COMMENTS
In strategy (a) we do not count spheres that can be obtained (by reflection) from the "extra" quintuples of spheres that appear in the previous generation.
LINKS
C. L. Mallows, Growing Apollonian Packings, J. Integer Sequences, 12 (2009), article 09.2.1.
EXAMPLE
Starting with five spheres with bends 0,0,1,1,1, the first derived generation has 5 spheres with bends 1,1,1,3,3, so a(2) = 9/3 = 3.
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Colin Mallows, Jan 13 2009
STATUS
approved