Write formula for calculation of the present value for a given future stream of income

The formula for calculating the present value (PV) of a future stream of income, assuming a constant interest rate (r) and constant cash flows (C) occurring at regular intervals (n), is given by the present value of an annuity formula:

\[ PV = \sum_{t=1}^{n} \frac{C}{(1 + r)^t} \]

Where:
- \( PV \) is the present value of the future stream of income.
- \( C \) is the constant cash flow received at each period.
- \( r \) is the interest rate per period (expressed as a decimal).
- \( n \) is the number of periods.

This formula essentially discounts each future cash flow back to its present value using the interest rate. Then, it sums up all the present values of the individual cash flows to determine the total present value of the income stream.