This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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. 2
 0, 0, 0, 0, 0, 0, 1, 1, 1, 2, 2, 3, 3, 4 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,10 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 16 23:49 EDT 2019. Contains 325092 sequences. (Running on oeis4.)