%I
%S 0,1,1,2,0,4,7,14,3,0,11,22,0,0,50,44,0,12,19,60,84,44,
%T 69,94,0,0,9,98,0,80,93,152,176,0,280,138,0,76,312,300,0,
%U 126,43,286,330,0,235,332,49,0,476,364,0,36,660,602,570,0,177,380,0,0,630,560,780,374,67,680,782,560,497,714,0,0,850,798,1232,468,395,1080,27,0,249,882,1360,172,1508,1430,0,600,1820,1058,1674,0,2090,1240,0,0,1518,1100
%N Difference between sums of quadratic residues and nonresidues modulo n that are coprime to n.
%F For prime n, a(n) = A228131(n) = A255644(n).
%F For prime n==1 (mod 4), a(n) = 0.
%F For prime n==3 (mod 4) and n>3, i.e., n=A002145(m) for m>1, a(n) = n*A002143(m).
%o (PARI) { A255643(n) = my(r); r=0; for(i=0,n1, if(gcd(i,n)>1,next); if(issquare(Mod(i,n)), r+=i, r=i) ); r }
%Y C.f. A228131, A255644
%K sign
%O 1,4
%A _Max Alekseyev_, Mar 01 2015
