BZOJ1968: [Ahoi2005]COMMON 约数研究

1 var i,n,ans:longint;
2 begin
3   assign(input,‘input.txt‘);assign(output,‘output.txt‘);
4   reset(input);rewrite(output);
5   readln(n);
6   for i:=1 to n do inc(ans,n div i);
7   writeln(ans);
8   close(input);close(output);
9 end.  

 1 const maxn=1000000+1000;
 2 var ans:int64;
 3     f,p:array[0..maxn] of int64;
 4     check:array[0..maxn] of boolean;
 5     i,n,tot:longint;
 6 procedure getprimes;
 7  var i,j,k:longint;
 8  begin
 9    fillchar(check,sizeof(check),false);
10    for i:=2 to n do
11     begin
12       if not(check[i]) then begin inc(tot);p[tot]:=i;end;
13       for j:=1 to tot do
14        begin
15          k:=i*p[j];
16          if k>n then break;
17          check[k]:=true;
18          if i mod p[j]=0 then break;
19        end;
20     end;
21  end;
22 procedure dfs(x,pos:int64);
23  var y:int64;i:longint;
24  begin
25    if pos>tot then exit;
26    y:=x;dfs(x,pos+1);
27    for i:=1 to 22 do
28     begin
29      y:=y*p[pos];if y>n then break;
30      f[y]:=f[x]*(i+1);
31      dfs(y,pos+1);
32     end;
33  end;
34 
35 procedure main;
36  begin
37    getprimes;
38    f[1]:=1;
39    dfs(1,1);
40    ans:=1;
41    for i:=2 to n do inc(ans,f[i]);
42    writeln(ans);
43  end;
44 
45 begin
46   assign(input,‘input.txt‘);assign(output,‘output2.txt‘);
47   reset(input);rewrite(output);
48   readln(n);
49   main;
50   close(input);close(output);
51 end.