|
%I #35 Jul 10 2015 06:40:32
%S 0,0,0,0,0,0,1,1,1,2,2,3,3,4
%N 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.
%H R. L. Graham and N. J. A. Sloane, <a href="http://neilsloane.com/doc/RLG/138.pdf">Penny-Packing and Two-Dimensional Codes</a>, Discrete and Comput. Geom. 5 (1990), <a href="http://dx.doi.org/10.1007/BF02187775">1-11</a>.
%H Kival Ngaokrajang, <a href="/A257481/a257481.pdf">Illustration of initial terms</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/HexagonalGrid.html">Hexagonal grid</a>
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Circle_packing">Circle packing</a>
%e For a(7), one circle can be completely enclosed by six surrounding circles, so a(7)=1, a(n)=0 for n<7.
%e For a(10), two circles can be completely enclosed by eight surrounding circles, so a(10)=2.
%Y Cf. A182619, A257594, A069813.
%K nonn,more
%O 1,10
%A _Peter Woodward_, Apr 26 2015
%E Edited by _N. J. A. Sloane_, May 18 2015
|
