仪仗队(points)

仪仗队(points)

【题意】

求存在多少个i,j互质的二元组(i,j)(0<=i,j<=n)

【输入】

一个数字表示n(n<=40000)

【输出】

一个数字，表示有多少个满足条件的二元组

枚举2到4000，对于每一个求其欧拉函数，求和乘二+3

program points;
var
  n,i,j,k,tot,ans:longint;
  prime:array [0..10001] of longint;
  yes:array [0..40001] of boolean;

begin
  assign(input,'points.in');
  reset(input);
  assign(output,'points.out');
  rewrite(output);
  read(n);
  dec(n);
  tot:=0;
  fillchar(yes,sizeof(yes),false);
  for i:=2 to n do
    if not yes[i] then
      begin
        inc(tot);
        prime[tot]:=i;
        yes[i]:=true;
        for j:=i to n div i do
          yes[i*j]:=true;
      end;
  ans:=0;
  for i:=2 to n do
    begin
      k:=i;
      j:=1;
      while (j<=tot)and(prime[j]<=i) do
        begin
          if i mod prime[j] = 0 then k:=k*(prime[j]-1) div (prime[j]);
          inc(j);
        end;
      ans:=ans+k;
    end;
  ans:=ans*2+3;
  writeln(ans);
  close(input);
  close(output);
end.