This is awesome - I bet you didn't know this

Letters 'a', 'b', 'c' & 'd' do not appear anywhere in the spellings of 1 to 99
(Letter 'd' comes for the first time in Hundred)

Letters 'a', 'b' & 'c' do not appear anywhere in the spellings of 1 to 999
(Letter 'a' comes for the first time in Thousand)

Letters 'b' & 'c' do not appear anywhere in the spellings of 1 to 999,999,999
(Letter 'b' comes for the first time in Billion)

And

Letter 'c' does not appear anywhere in in the spellings of entire English Counting

Folder Lock without any Software

Open Notepad and copy the below code and save as locker.bat. On first click, it will create folder with name Locker automatically. Don't forget to change your password in the code; it is shown as "type your password here".
After creation of Locker folder, again click on the locker.bat  it will ask.press Y then Locker folder will be disappeared. To get back the folder click on locker.bat. and give ur password.

 

cls
@ECHO OFF
title Folder Locker
if EXIST "Control Panel.{21EC2020-3AEA-1069-A2DD-08002B30309D}" goto UNLOCK
if NOT EXIST Locker goto MDLOCKER
:CONFIRM
echo Are you sure u want to Lock the folder(Y/N)
set/p "cho=>"
if %cho%==Y goto LOCK
if %cho%==y goto LOCK
if %cho%==n goto END
if %cho%==N goto END
echo Invalid choice.
goto CONFIRM
:LOCK
ren Locker "Control Panel.{21EC2020-3AEA-1069-A2DD-08002B30309D}"
attrib +h +s "Control Panel.{21EC2020-3AEA-1069-A2DD-08002B30309D}"
echo Folder locked
goto End
:UNLOCK
echo Enter password to Unlock folder
set/p "pass=>"
if NOT %pass%== type your password here goto FAIL
attrib -h -s "Control Panel.{21EC2020-3AEA-1069-A2DD-08002B30309D}"
ren "Control Panel.{21EC2020-3AEA-1069-A2DD-08002B30309D}" Locker
echo Folder Unlocked successfully
goto End
:FAIL
echo Invalid password
goto end
:MDLOCKER
md Locker
echo Locker created successfully
goto End
:End