Binary – 2 digits (0 1)
Start with 0, increment to 1, then go back to 0 and increment the next column to the left
Example:  0110 0001

Hexadecimal – 16 digits (0 1 2 3 4 5 6 7 8 9 A B C D E F)
Count up to the last digit, then return to zero and increment the next column to the left
Example:  0x61

Decimal – 10 digits (0 1 2 3 4 5 6 7 8 9)
Increase each digit in the right-most place column until you reach 9, then you return to zero and increment the next column to the left.
Example:  97 puttygen download