To enable full mesh IBGP within that Transit AS, how many IBGP sessions are required?

A Transit AS contains 10 routers. To enable full mesh IBGP within that Transit AS, how many IBGP sessions are required?

A.
10

B.
28

C.
45

D.
50

E.
100

Explanation:
full mesh = (n)(n-1)/2 = 10*9/2 = 45