OFFSET
0,2
COMMENTS
Experimentally observed dense bcc clusters of gold contain 1, 9, 59, 169, 339, 701 and 1243 nanoparticles (N.G. Khlebtsov, Fig. 32 and text on p. 208), exactly matching the first 7 terms of the sequence.
First 5 terms are the same as A276450.
LINKS
Yuriy Sibirmovsky, Table of n, a(n) for n = 0..50
N. G. Khlebtsov, T-matrix method in plasmonics: An overview, J. Quantitative Spectroscopy & Radiative Transfer 123 (2013) 184-217.
EXAMPLE
The origin has norm 0, thus a(0)=1. The distance to the 8 vertices of the cube from the origin is 1, because the edge of the cube is 2/sqrt(3). Thus a(1)=9.
MATHEMATICA
DecM[A_]:=A[[1]]^2+A[[2]]^2+A[[3]]^2;
Do[N1=0; N2=0;
Do[A={l, k, j};
B={l+1/2, k+1/2, j+1/2};
If[DecM[A]<=3/4r^2, N1+=1];
If[DecM[B]<=3/4r^2, N2+=1], {l, -r-1, r+1}, {k, -r-1, r+1}, {j, -r-1, r+1}];
Print[r, " ", N1+N2], {r, 0, 20}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Yuriy Sibirmovsky, Sep 11 2016
STATUS
approved