My friend sent me this tricky puzzle...
Please explain the reason for the mistake in the number sequence - what is it trying to communicate?
8139, 8140, 8141, 5493, 8143, 8144
Although not a number sequence puzzle, there is a sequence of some kind, albeit brief, lodged in here that will reveal the intended answer if noticed. Pay close attention to the Knowledge tag.
The history tag is certainly valid for this puzzle.