A257481 Consider a hole-less cluster of n circles in the hexagonal lattice packing of circles; a(n) is the maximal number of circles that touch 6 circles.

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

Offset

1,10

Links

Table of n, a(n) for n=1..14.

R. L. Graham and N. J. A. Sloane, Penny-Packing and Two-Dimensional Codes, Discrete and Comput. Geom. 5 (1990), 1-11.

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: A363826 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