21087005 has 4 divisors (see below), whose sum is σ = 25304412. Its totient is φ = 16869600.

The previous prime is 21086981. The next prime is 21087019. The reversal of 21087005 is 50078012.

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

It can be written as a sum of positive squares in 2 ways, for example, as 14394436 + 6692569 = 3794^2 + 2587^2 .

It is not a de Polignac number, because 21087005 - 2¹⁸ = 20824861 is a prime.

It is a Duffinian number.

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 3 ways as a sum of consecutive naturals, for example, 2108696 + ... + 2108705.

It is an arithmetic number, because the mean of its divisors is an integer number (6326103).

Almost surely, 2^21087005 is an apocalyptic number.

It is an amenable number.

21087005 is a deficient number, since it is larger than the sum of its proper divisors (4217407).

21087005 is an equidigital number, since it uses as much as digits as its factorization.

21087005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4217406.

The product of its (nonzero) digits is 560, while the sum is 23.

The square root of 21087005 is about 4592.0589064166. The cubic root of 21087005 is about 276.2729088377.

The spelling of 21087005 in words is "twenty-one million, eighty-seven thousand, five".