> For the complete documentation index, see [llms.txt](https://trizen.gitbook.io/sidef-lang/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://trizen.gitbook.io/sidef-lang/programming_tasks/t/truncatable_primes.md).

# Truncatable primes

```ruby
func t_prime(n, left=true) {
    var p = %w(2 3 5 7);
    var f = (
        left ? { '1'..'9' ~X+ p }
             : { p ~X+ '1'..'9' }
    )
    n.times {
        p = f().grep{ .to_i.is_prime }
    }
    p.map{.to_i}.max
}
 
say t_prime(5, left: true)
say t_prime(5, left: false)
```

#### Output:

```
998443
739399
```