Answer: 5 branches and 16 birds.
Step-by-step explanation:
If the number of birds is B, and the number of branches is N.
First we have the equation:
B = 3*N + 1
(3 birds per branch + 1 that was flying around)
for the second equation we have:
B = 4*(N - 1)
(4 birds per branch, but one branch had no birds on it, so there are N -1 branches used)
now we can write:
3*N + 1 = 4*(N - 1)
3*N + 1 = 4*N - 4
4 + 1 = 4*N - 3*N
5 = N
So we had 5 branches, now we can replace it in one of the equations and find the number of birds.
B = 3*N + 1 = 3*5 + 1 = 16

As

, the sequence

converges to zero.
If you're talking about the infinite series

well we've shown by comparison that this series must also converge because we know any geometric series

will converge as long as

.