Effective interest paid - need formula/function

I would like to calculate the effective interest paid on a lease. If the
asset value is $55k, and the lease payments are $2,519 for 2 years with a
residual asset value of $1 at the end of the lease, what is the effective
interest rate? Note that the first payment is double ($5,038), with 22
monthly payments thereafter.

Since your payments are not equal, you will want to use the IRR function. This would require you to list out all of the payments as such:

55000
-5038
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
-2519
0
1

=IRR(above range)

The answer is 0.84% x 12 = 10%

Of course, I assumed you had the "free" month at the end....instead of immediately after the double-month at the beginning.