21000005 has 8 divisors (see below), whose sum is σ = 27138552. Its totient is φ = 15507648.

The previous prime is 20999999. The next prime is 21000037. The reversal of 21000005 is 50000012.

It can be written as a sum of positive squares in 4 ways, for example, as 51076 + 20948929 = 226^2 + 4577^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21000005 - 2⁶ = 20999941 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 20999956 and 21000001.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 161474 + ... + 161603.

It is an arithmetic number, because the mean of its divisors is an integer number (3392319).

Almost surely, 2^21000005 is an apocalyptic number.

It is an amenable number.

21000005 is a deficient number, since it is larger than the sum of its proper divisors (6138547).

21000005 is a wasteful number, since it uses less digits than its factorization.

21000005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 323095.

The product of its (nonzero) digits is 10, while the sum is 8.

The square root of 21000005 is about 4582.5762405005. The cubic root of 21000005 is about 275.8924395343.

Adding to 21000005 its reverse (50000012), we get a palindrome (71000017).

The spelling of 21000005 in words is "twenty-one million, five", and thus it is an aban number and an uban number.