Re:Legible Mathematics: Sketches of interactive arithmetic f...
by Someone on Monday February 24, 2020 @01:41PM
(#22406979)
That started at least with Ada, in 1979 (https://softwareengineering.stackexchange.com/a/403959).
Traditional FORTRAN ignores all spaces, so one can write a million as 1 000 000 there, C++14 allows apostrophes (https://en.wikipedia.org/wiki/Decimal_separator#Data_versus_...)
a = 100_000 b = 1_000_000