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A333572 a(n) is the number of Gaussian integers z with 0 < |z| <= n/2.

%I A333572 #14 Mar 29 2020 17:12:19
%S A333572 0,4,8,12,20,28,36,48,68,80,96,112,136,148,176,196,224,252,292,316,
%T A333572 348,376,420,440,488,528,576,612,664,708,748,796,860,900,972,1008,
%U A333572 1084,1128,1200,1256,1312,1372,1456,1516,1596,1652,1740,1792,1884,1960,2052,2120
%N A333572 a(n) is the number of Gaussian integers z with 0 < |z| <= n/2.
%H A333572 Robert Israel, <a href="/A333572/b333572.txt">Table of n, a(n) for n = 1..2000</a>
%p A333572 N:= 100: # for a(1)..a(N)
%p A333572 V:= Vector(N):
%p A333572 for x from 1 to N/2 do
%p A333572   for y from 0 to x do
%p A333572     v:= ceil(2*sqrt(x^2+y^2));
%p A333572     if v > N then break fi;
%p A333572     if y=x or y=0 then V[v]:= V[v]+4 else V[v]:= V[v]+8 fi
%p A333572 od od:
%p A333572 ListTools:-PartialSums(convert(V,list)); # _Robert Israel_, Mar 29 2020
%Y A333572 Cf. A004018, A232705, A333462, A333573.
%K A333572 nonn
%O A333572 1,2
%A A333572 _Hugo Pfoertner_, Mar 27 2020