%I #8 Feb 11 2020 02:04:20
%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 non-residues 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,n-1, if(gcd(i,n)>1,next); if(issquare(Mod(i,n)), r+=i, r-=i) ); r }
%Y Cf. A228131, A255644.
%K sign
%O 1,4
%A _Max Alekseyev_, Mar 01 2015