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21 in Binary

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What is 21 in binary? Below we show you the result of the decimal to binary conversion straightaway 🙂


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If you want to know how to convert 21 to binary please read the instructions on the homepage.

Binary 21 = 101012
The binary for 21 is 10101

As any other integer, 21 can be written as sum of potencies to the power of 2, known as binary code. Here’s the proof that 10101 is the binary of 21:

1×2^4 + 0x2^3 + 1×2^2 + 0x2^1 + 1×2^0 = 21

Yet, make sure to learn about 21 in binary signed in the next section.

If you like to know the binary code for any other decimal number than 21 please use our converter above.

Enter any number and hit Decimal to Binary.

Similar decimal to binary conversions on this web site include:

Convert 21 to Binary

Now you already know the most important thing about 21 in binary form. 10101 is binary 21. That is if the binary in unsigned.

If 21 in binary is signed such as with two’s complement, then the binary code has a number of trailing zeroes, e.g. 00010101 in which the leftmost bit is the sign bit, followed perhaps by more trailing 0’s, and then by magnitude bits.

The reason to have the binary 21 signed is to accommodate for negative numbers, in which case the sign bit is 1 in our example.

Therefore, minus 21 signed using two’s complement, will start with one or more 1’s, but the exact code for -21 decimal to binary depends on the signed number representation system and number of bits available.

Here you can convert binary to decimal. If you like to know what decimal 21 is on other number systems, we have that too:

21 in Hexadecimal = 1516
21 in Octal = 258


21 in binary is 10101 usually, that is if not signed. If you want to know more about signed number representations look it up on Wikipedia for example.

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