> 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/l/largest_prime_factor.md).

# Largest prime factor

```ruby
var n = 600851475143
 
say gpf(n)             #=> 6857
say factor(n).last     #=> 6857
```