21
The binary number 10101 represents 21.
10101
10101
100000002 = 27 = 128 in denary (or decimal).
10101
21 = 10101
10101
10101
The number 21 in binary is 10101
The number 21 in binary is 10101
It is 01101010.
A denary number is a number based on the ten digits, from 0 to 9. This is in contrast to the binary system used in computing, which consists entirely of 0s and 1s.