How many ordered sets of positive integers are there if:
1.Their sum is less than 6
2. There are at most 4 addends
3. None of them is composite.
Please specify how quick were you to get the right answer.
(In reply to Solution spoiler
a. order counts
b. You mentioned only pairs, - where are the triplets ,quadruplets and quintuplets? 111 123 132 231 11111 1211 1112 etc
Now list them ALL!