

A257481


Consider a holeless cluster of n circles in the hexagonal lattice packing of circles; a(n) is the maximal number of circles that touch 6 circles.


2



0, 0, 0, 0, 0, 0, 1, 1, 1, 2, 2, 3, 3, 4
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OFFSET

1,10


LINKS

Table of n, a(n) for n=1..14.
R. L. Graham and N. J. A. Sloane, PennyPacking and TwoDimensional Codes, Discrete and Comput. Geom. 5 (1990), 111.
Kival Ngaokrajang, Illustration of initial terms
Eric Weisstein's World of Mathematics, Hexagonal grid
Wikipedia, Circle packing


EXAMPLE

For a(7), one circle can be completely enclosed by six surrounding circles, so a(7)=1, a(n)=0 for n<7.
For a(10), two circles can be completely enclosed by eight surrounding circles, so a(10)=2.


CROSSREFS

Cf. A182619, A257594, A069813.
Sequence in context: A099964 A094440 A093736 * A014589 A071456 A071505
Adjacent sequences: A257478 A257479 A257480 * A257482 A257483 A257484


KEYWORD

nonn,more


AUTHOR

Peter Woodward, Apr 26 2015


EXTENSIONS

Edited by N. J. A. Sloane, May 18 2015


STATUS

approved



