在100以内能被3整除的数中最小是3，最大是993至99共有(99-3)/3+1＝33个这些数的和是（3+99）*33/2＝1683其中能被3也能被7整除的数（也就是能被21整除的数）最小为21，最大为84，共有(84-21)/21+1=4个其和为(84+21)*4/2=210最后的答案是1683-210=1473
void main(){int i,s=0;for(i=3;i<=100;i++){if(i%3==0&&i%7!=0)s+=i;}printf("%d",s);}答案是1473.我运行过．
1473Private Sub Command1_Click()Dim a, sum As Integersum = 0For a = 1 To 100 If a Mod 3 = 0 And a Mod 7 <> 0 Then sum = sum + a End IfNextPrint sumEnd Sub
#include "stdio.h"void main(){int i,sum=0;for(i=0;i<101;i+=3) if(i%7) sum+=i;printf("The sum is:%d",sum);}