Hi I have a one time pad which uses a key k as : -

    F(r) || F(r+1) || F(r+2) .....
    
I have to prove that if F(r) is RSA encryption algorithm . 

    F(r) = r^e mod p where e and p are known , e = 3
If we know the F(r), F(r+1) and F(r+2) we can calculate the subsequent key sequence

Is there any obvious relation between F(r+3) and F(r),F(r+1),F(r+2) I dont  see it?