21007 has 4 divisors (see below), whose sum is σ = 24016. Its totient is φ = 18000.

The previous prime is 21001. The next prime is 21011. The reversal of 21007 is 70012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21007 - 2⁷ = 20879 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20984 and 21002.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1494 + ... + 1507.

It is an arithmetic number, because the mean of its divisors is an integer number (6004).

2²¹⁰⁰⁷ is an apocalyptic number.

21007 is a deficient number, since it is larger than the sum of its proper divisors (3009).

21007 is an equidigital number, since it uses as much as digits as its factorization.

21007 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3008.

The product of its (nonzero) digits is 14, while the sum is 10.

The square root of 21007 is about 144.9379177441. The cubic root of 21007 is about 27.5923068946.

Adding to 21007 its reverse (70012), we get a palindrome (91019).

The spelling of 21007 in words is "twenty-one thousand, seven", and thus it is an iban number.