regardless of whether it makes sense to say that treating zero as a number was 'the first abstraction' or not†, ancient mesopotamians did not treat zero as a number. even noble fibonacci didn't consider it as a number or even a digit:
> The nine Indian figures are: 9 8 7 6 5 4 3 2 1. With these nine figures, and with the sign 0 (...) any number may be written.
i'm not sure when it became conventional to consider it a number rather than the absence of one; it might not have been until the early modern era
> The nine Indian figures are: 9 8 7 6 5 4 3 2 1. With these nine figures, and with the sign 0 (...) any number may be written.
i'm not sure when it became conventional to consider it a number rather than the absence of one; it might not have been until the early modern era
https://news.ycombinator.com/item?id=40917674 suggests that european mathematicians still hadn't agreed that 1 was a number until the early modern era
______
† it doesn't