It's true in base 4, called the 'quaternary numeral system', where counting is done this way. 1,2,3,10,11,12,13,20,21,22,23,30,31,32,33,100,101,102,... Only the digits 0,1,2, and 3 are used in the quaternary numeral system. 2+2=10 in the quaternary system is not read "two plus two equals ten", it's read "two plus two equals 'one zero'". "10" in quaternary is really the same as four in the decimal numeral system, 11 is the same as five, etc. When counting up, when you get to a 3, you change it to 0 and add 1 to the next digit to the left if it is not 3. If it is 3, you change it to 0, and add one to the digit left of it. When all the digits are 3's, the next number will have one more digit, and will begin with 1 and all the rest zeros. Go here to read about it: https://en.wikipedia.org/wiki/Quaternary_numeral_system Edwin