Brain Buster

Chicken McPieces Madness

Chicken McPieces come in boxes of 6, 9 and 20.

Therefore, it is possible to purchase 15 McPieces (ie. 6 + 9) but not 14.

Determine all possible numbers of McPieces you cannot purchase.

Hint: Here are the first couple: 1, 2, 3, 4, 5, 7, 8, 10 ...