The gospel of Matthew claims that there were 14 generations from Abraham to David, 14 from David to the exile to Babylon, and 14 from the exile to the Messiah. There is some ambiguity in that statement: When you say there were N generations from X to Y, are you counting both X and Y as part of those N generations, or are you counting just one of them, or neither of them? Matthew does list the generations he’s talking about, though, so we can look at his list to get a better idea of what exactly he means.

Looking at that list of ancestors, it seems like the author intends to count both the first and the last person as part of the group of 14 generations. We can also see that he is including the last generation in one group of 14 as the first generation in the next group of 14. And that when Matthew talks about the generation of the exile to Babylon, he’s talking about Jeconiah, AKA Jehoiachin.

But there’s a problem with Matthew’s list: The second group actually contains 15 generations, not 14. You could count it as 14 if you interpret that number as a difference between generations, rather than inclusive of both the first and last person listed, but then you would have to say the other groups were just 13 generations each. Whichever way you count them, Matthew’s second group does not have the same number of generations as his first and third, contrary to what he claims after listing them.