let pascal rows = // Create pascal's triangle as a jagged 2d list
  let pascalRow row = //Calculates a row of the triangle
    List.init (row + 1) (fun i -> i) //Create list of which the element values are the index
    |> List.scan (fun prev index -> //prev = previous element of this row, index=current element number of row
      if index = 0 then //Special case for the 1st element
        1
      else //Calculate the element at this index based on the previous value
        prev * (row + 1 - index)/index) 1
    |> List.tail //Remove the collected value to obtain the row
  List.init rows pascalRow // Create a new array of pascal row

pascal 3 //Four rows of Pascal's triangle, including row 0,1,2
// [[1]; [1; 1]; [1; 2; 1]]