Version 1.5 of package Num3-Mode has just been released in GNU ELPA. You can now find it in M-x list-packages RET.
Num3-Mode describes itself as: ========================================== highlight groups of digits in long numbers ========================================== More at https://elpa.gnu.org/packages/num3-mode.html ## Summary: Num3 is a minor mode that makes long numbers and other numeric data more readable by highlighting groups of digits in a string when font-lock is on. For example, an integer ‘28318530’ would be split into 3-digit-long groups as ‘(28)(318)(530)’ and then each group highlighted using alternating face. This improves readability of the number by clearly denoting millions, thousands and ones. Besides integers and real numbers, the mode also supports dates in ‘20151021T0728’ format. ## Recent NEWS: [Not provided 🙁]
