if you have a array of numbers and want to identify
which of those numbers add up to a specified value, is there a function
in excel (or has anyone written one) that can help find the correct
combination of numbers.

eg in a simple example; if the array of values was 2,3,5,6 and the
specified value was 9, we know the only combination of numbers from this
array that would sum to give the value 9 are 6 & 3, however
with larger arrays of numbers (30) or more, it would be more difficult
solve the problem manually.