Actually I think your math is right (You can't be sure there is equal weight to the probabilities though, that would change math a bit) Either way probably pretty unlikely to go four in a row But what you are missing is that in any diverse random data set there will always be unlikely patterns cropping up all the time. You saw one pattern and did the numbers and yes it is indeed individually unlikely, but the Hunter Titan Engram and Weapon patterns have not been unusual at all recently. You calculated the chance of four straight voidfangs on these four specific weeks. But the chance of at least one of these items going four in a row at some point in the first 3 months of the game is relatively good. Too bad for warlocks they drew the short straw!