21 Senary to Binary
21 senary = 1101 binary
21 written in binary is 1101, the number 13 in everyday decimal.
21 senary = 1101 binary
How to convert 21 to binary
Step 1: Senary to decimal
Multiply each digit by 6 to the power of its position (0 on the right), then add:
| Digit | Place value | Digit × place |
|---|---|---|
2 | 61 = 6 | 12 |
1 | 60 = 1 | 1 |
12 + 1 = 13
Step 2: Decimal to binary
Divide by 2 repeatedly and keep the remainders. Reading the remainders from the last one to the first gives the binary digits:
| Division | Quotient | Remainder (digit) |
|---|---|---|
| 13 ÷ 2 | 6 | 1 |
| 6 ÷ 2 | 3 | 0 |
| 3 ÷ 2 | 1 | 1 |
| 1 ÷ 2 | 0 | 1 |
Result: 13 = 1101 in binary.
21 (senary) in other systems
| Decimal | 13 |
| Roman numerals | XIII |
| Hexadecimal | D |
| Octal | 15 |
| Duodecimal | 11 |
| Ternary | 111 |
| Base 36 | D |
| Vigesimal | D |
| Quaternary | 31 |
| Quinary | 23 |
Nearby senary to binary conversions
| 12 to binary | 1000 |
| 13 to binary | 1001 |
| 14 to binary | 1010 |
| 15 to binary | 1011 |
| 20 to binary | 1100 |
| 22 to binary | 1110 |
| 23 to binary | 1111 |
| 24 to binary | 10000 |
| 25 to binary | 10001 |
| 30 to binary | 10010 |
About the number 13
- 13 is an odd number.
- 13 is a prime number.
- Written in binary it needs 4 bits, so it fits in one byte.
Reverse conversion
Frequently asked questions
What is 21 in binary?
21 in senary is 1101 in binary (the number 13 in decimal).