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A154641
a(n) is the ratio of the sum of the bends of the spheres that are added in the n-th generation of Apollonian packing of three-dimensional spheres, using "strategy (a)" to count them (see the reference), to the sum of the bends of the initial five mutually tangent spheres.
2
1, 3, 20, 108, 630, 3570, 20460
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
For other sequences relating to the 3-dimensional case, see A154638-A154645.
Sequence in context: A119693 A158243 A139471 * A178711 A257067 A108911
KEYWORD
hard,more,nonn
AUTHOR
Colin Mallows, Jan 13 2009
STATUS
approved