> 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/s/semiprime.md).

# Semiprime

Built-in:

```ruby
say is_semiprime(2**128 + 1)   #=> true
say is_semiprime(2**256 - 1)   #=> false
```

User-defined function, with trial division up to a given bound `B`:

```ruby
func is_semiprime(n, B=1e4) {

    with (n.trial_factor(B)) { |f|
        return false if (f.len > 2)
        return f.all { .is_prime } if (f.len == 2)
    }

    n.factor.len == 2
}

say [2,4,99,100,1679,32768,1234567,9876543,900660121].grep(is_semiprime)
```

## Output:

```
[4, 1679, 1234567, 900660121]
```