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A240692 Squared radii of circles which exactly encircle clusters in the A2 lattice in increasing order. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..41.

Rajan Murthy, Generating code for the sequence (Scilab)

EXAMPLE

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).

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.

Sequence in context: A312984 A312985 A312986 * A022130 A042125 A041905

Adjacent sequences:  A240689 A240690 A240691 * A240693 A240694 A240695

KEYWORD

nonn

AUTHOR

Rajan Murthy, Apr 10 2014

STATUS

approved

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Last modified November 17 18:24 EST 2019. Contains 329241 sequences. (Running on oeis4.)