0

I am generating the sequence 1,3,8,22,60,....

upto 10^9 the term mod of 10^9+7;

However my code is giving inaccurate answers for large value of n.

The formula I am using is ((1+Q)^(n+1)-(1-Q)^(n+1))/(4*Q)

Here Q is sqrt (3)

Here is my code.Can someone point out the error in the code or any ways to remove this problem.

Any help will be highly appreciated.

```
#include <iostream>
#include<stdio.h>
#define big long long int
#define foo(b) static_cast<big>(b)
big ro(long double x)
{
if(x-(big)x>=0.5)
{
return x+1;
}
else
return x;
}
big m=1000000007;
long double Q=1.7320508075688772935274463415058723669428052538103806;
using namespace std;
long double mod(long double a,big b)
{
big result = static_cast<big>( a / b );
return a - static_cast<long double>( result ) * b;
}
long double modex(long double a,big b, big n){
long double r = 1;
while (1){
if (b&1)
r = mod(mod(mod(r,m),m) * a,m) ;
b /= 2;
if (!b )
break;
a = mod(mod(a,m) *mod( a,m), m);
}
return r;
}
int main()
{
#ifndef ONLINE_JUDGE
freopen("in.txt","w",stdout);
cout<<10000<<endl;
for(big i=1;i<=10000;i++)
//cout<<1000000000<<endl;
cout<<i<<endl;
freopen("out.txt","w",stdout);
freopen("in.txt","r",stdin);
#endif
big t,n;
cin>>t;
while(t--)
{cin>>n;
long double ans1= (modex((1.00000000000 + Q),(1+n),m));
long double ans2 = (modex((1.0000000000 - Q),(1+n),m )) ;
long double ans3=(1/ (4*Q));
long double ans=(ans1-ans2);
//ans=ans/ans3;
cout<< ro(ans*ans3)<<endl;
//cout<<ans<<endl;
}
return 0;
}
```