How to calculate the ⌉ operator?

Question

In a book about finance, the following formula appears:

$$\large a_{10 \,⌉\, 0.04}$$

What is this ⌉ operator and how to read / calculate it?

Answer 1

This just a notation in Actuarial sciences

$a_{\overline{n|}i} := v + v^2 + \cdots + v^n = \frac{1-v^n}{i}$ , where $v:=\frac{1}{i+1}$

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So,

$a_{\overline{10|}0.04}=\frac{1-(1+0.04)^{-10}}{0.04} \approx 8.111$