Here's my solution to PE5.

(**

* Gives true when n is evenly divisible for each number in list

*

* @method EvenlyDivisible

* @param {int list} list

* @param {int} n

* @return {bool} True when number is evenly divisible for each number in list, else false

*)

let EvenlyDivisible list n = list |> List.forall ((%) n >> (=) 0)

(**

* Active pattern for Divisible/Undivisible

*

* @method Divisible|Undivisible

* @param {int} n

* @return {Choice<unit,unit> Divisible when n is evenly divisible with every number up to 20, else Undivisible

*)

let (|Divisible|Undivisible|) n =

if (EvenlyDivisible [11;12;13;14;15;16;17;18;19;20] n) then Divisible

else Undivisible

(**

* Find the first number that is "Divisible"

*

* @method find

* @param {int} n

* @return {int} First number that is considered "Divisible"

*)

let rec find n =

match n with

| Divisible -> n

| _ -> find (n + 1)

// Run

find 21

Are there parts of the code missing due to formatting problems?

If not, you should learn some more about the basics of functional programming first, for example here: [link:en.wikibooks.org]