A240692 Squared radii of circles which exactly encircle clusters in the A2 lattice in increasing order.

0, 4, 9, 13, 21, 25, 28, 36, 39, 43, 49, 57, 63, 64, 67, 76, 81, 84, 91, 93, 97, 109, 111, 117, 121, 124, 129, 133, 144, 147, 148, 156, 157, 163, 171, 175, 183, 189, 193, 196, 199, 201

Offset: 0

Author

Rajan Murthy, Apr 10 2014

Keywords

• nonn

Examples

			For n = 1, a(1) = 4, the squared distance to the corners furthest from the deep hole of three hexagons which share the deep hole as a corner.
For n= 3, a(3) = 13, the squared distance to the furthest corners of the 6 hexagons third most distant from the deep hole - which, when added to the 3 that are closest and the 3 that are second-closest, yields a total of 12, which is A038588(3).
		

Links

• Rajan Murthy, Generating code for the sequence (Scilab)

Crossrefs

A038588(n) gives the corresponding cluster size starting at n = 1 (the first positive radius circle);

A000404 is the analog for a Cartesian lattice.