Nerd blog post!
Most permutation algorithms rely on the previous permutation to generate the next one. This makes it inefficient to get a specific permutation, like the 100,000th if you don't have the 99,999th.
So I wrote an #algorithm to do it.
https://blog.edwardloveall.com/random-access-permutations
Not being trained in computer science, I am unreasonably proud of this.