The Number
21
Twenty-One
In Base 7 Septenary Is
307
The numbers with a 7 subscript use Base 7 Septenary notation.
For more familiar numbers: See Twenty-One in Base 10 Decimal
Nearby Numbers
Positive, nonzero integers within three units
Scientific Notation
Scientific notation expresses a quantity as the product of its significand with 10 raised to an integer exponent.
2.1e1
Reciprocal
A number multiplied with its reciprocal is one.
0.022222222222222222227
The reciprocal of 21 in Base 7 Septenary.
Palindrome?
A numerical palindrome has the same value when all of its digits are reversed.
The number 307 is not a palindrome.
Not A Prime Number
A prime number is a positive integer that is divisible only by itself and one.
Twenty-one is a composite number with 4 total factors (including 1 and itself). See primes in Base 7 Septenary
A Composite
Composites have more than just these two factors.
Twenty-one is a composite number with 4 total factors (including 1 and itself).
Prime Factors
The number twenty-one has the following 2 prime factors:
Prime Factorization
The prime factorization of a positive integer is the unique list of prime factors together with their multiplicities
371
·
1071
= 307
Base Conversions
The number twenty-one in 35 different bases