expand a number vector according to the adjacent two numbers

## Arguments

- v
number vector

- n_div
how many divisions expanded by two numbers

- .unique
only keep unique numbers

## Examples

```
adjacent_div(10^c(1:3), n_div = 10)
#> [1] 10 20 30 40 50 60 70 80 90 100 100 200 300 400 500
#> [16] 600 700 800 900 1000
```