Always failed to remember it using numbers 🙁
Check this out: Ive found this in some howto website too and I hope you too can made up your own imagination to remember below MATH:)
CHMOD can also to attributed by using Numeric Permissions:
400 read by owner
040 read by group
004 read by anybody (other)
200 write by owner
020 write by group
002 write by anybody
100 execute by owner
010 execute by group
001 execute by anybody
The above numeric Permissions can be added to set a certain permission, for example, a common HTML file on a UNIX server to be only viewed over the Internet would be:
CHMOD 755 file.htm
Which would be the following 400+040+004+200+020+100+010+001 = 775 where you are giving all the rights but the capability for anyone to edit your file.htm.
Easy eh? Practise it, and you will use to it. And find it easier than when you use character.