Concatenating list from a function to another recursive function in OCaml

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So I am trying to code a relatively simple function in OCaml which takes an integer n and a list of integers up to 5 and then repeats all integers above 1 in said list n times.

I already have an existing function repeat which repeats whatever I feed it n times

let rec repeat : int -> 'a -> 'a list =
 fun n a ->  
  match n with  
  | 0 -> []  
  | h -> a :: repeat (h-1) a ;;

Now here is the code for the function called Pentograph

let pentograph : int -> int list-> int list =
  fun n letter ->
    match letter with 
    |[] -> []
    |h::t -> if h>1 then List.concat[(repeat n h);pentograph n t] else List.conca[h;pentograph n t];;

I get the following error:

Error: Unbound value pentograph

On trying to use the :: operator I get an error too as I can not use it to concat 2 lists.

Please help me figure out a solution to this problem!

ocaml