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Cod sursa(job #109642)
program pairs;
var a:array[1..2000] of longint;
k,n,i,j,rez,min:longint;
f,g:text;
prime:boolean;
begin
assign(f,'pairs.in'); assign(g,'pairs.out');
reset(f); rewrite(g);
read(f,n);
if n>2000 then writeln(g,n*(n-1) div 2) else
begin
for i:=1 to n do read(f,a[i]);
rez:=n*(n-1) div 2;
for k:=1 to n-1 do
for j:=k+1 to n do
begin
prime:=true;
if a[k]>a[j] then min:=a[j] else min:=a[k];
i:=3;
if ((a[j] mod 2=0) and (a[k] mod 2=0)) or
((a[j] mod 3=0) and (a[k] mod 3=0)) or
((a[j] mod 5=0) and (a[k] mod 5=0)) then prime:=false
else
while (i<=min div 2) do
begin
if (a[k] mod i=0) and (a[j] mod i=0) then begin prime:=false; i:=(min div 2)+1; end;
i:=i+2;
end;
if not prime then rez:=rez-1;
end;
write(g,rez);
end;
close(f); close(g);
end.