Help me with my inability to see a simple solution

[william humphrey]

My math skills are terrible but this is something I can do in excel but
which should also be easy to do with a nested array in livecode. I want to
build a function that returns the numbers that are out of sequence in a list
of numbers. Say you are given (3,4,5,6,6,7,8,9,10,12,13,13,14) and the
function should return:

(1,2,11 - missing)
(6,13 - duplicate)

Can someone please help me write this function?

Thanks in advance.