OFFSET
0,2
COMMENTS
In strategy (b) we count all spheres that can be generated (by reflection) from all quintuples that appeared 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