for(int j1=n-1;j1>=n-i1+1;--j1) //j1=9 j1=9 c(10,i1)
s1=(s1*j1)/(n-j1+1); //s1=(10*9)/2
return s1; }
int main()
{
s=n+1; //11
for(int i=2;i<=n;i++)
{
//cout<<" "<<co(i)<<endl;
s=s+co(i);
}
printf("S=%d",s);
}
/
答案：S=
/
原文：https://blog.51cto.com/1443208/2361840