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

Author

Peter Woodward, Apr 26 2015

Keywords

• nonn
• more

Examples

			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.
		

Links

• 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

Crossrefs

Cf. A182619, A257594, A069813.

Extensions

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