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%I #23 Mar 31 2018 14:41:27
%S 5,12,20,24,36,44,40,52,60,68,72,68,92,96,100,100,108,120,124,132,128,
%T 148,140,144,172,180,180,168,180,204,192,212,204,220,240,212,244,232,
%U 268,260,248,276,268,292,288,276,300,296,316,324,348,336,324,348,336
%N Number of pairs of integers (x,y) with n^2 <= x^2+y^2 <= (n+1)^2.
%C Number of integer Cartesian grid points covered by a ring around the origin with width 1 and outer radius n. Also, number of Gaussian integers z=a+bi satisfying n-1 <= |z| <= n. - _Ralf Stephan_, Nov 28 2013
%H T. D. Noe, <a href="/A047077/b047077.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Ga#gaussians">Index entries for Gaussian integers and primes</a>
%F a(n) = A000328(n+1) - A051132(n).
%t a[n_] := Sum[SquaresR[2, k], {k, n^2, (n+1)^2}]; Table[a[n], {n, 0, 54}] (* _Jean-François Alcover_, Oct 15 2012 *)
%Y Cf. A000328, A051132, A077770.
%K easy,nice,nonn
%O 0,1
%A Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Jan 26 2000
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