Hi, i have a basic understanding of this question, however I am trying to learn from it and I have no idea where a few values are coming from. Okay so here it is:

The Smith's have just purchased a new piece of property for a summer home for $122,000.00 and they are able to provide a $26,000.00 down payment. The loan is to be amortised over a 13-year period at a 6.5% interest rate and a 5 year term.
How large is their monthly payment? n = 13*12 = 120 (the equation to get 120=10*12)
semi-annual rate = 6.5%/2 = 3.25%
Eff monthly rate = (1.0325)^(1/6)-1=0.53%
Size of loan (PV) = 122K - 26K = $96,000
A = PV [ i / (1 - (1 / (1+i)^n))] =$1,086

I understand the semiannual rate, effective i rate, size of the loan, how ever the 120 is used the Annutity as n. why is is n=12*13 = 156? but the answer is 120? I am totally confused as to this matter. Any light on this would appreciated. 13 would be the years and 12 would be the months right? so 156 months? Is the 10 from 5 year term x 2 because it is semiannual?
Thanks again