21090587 has 4 divisors (see below), whose sum is σ = 24103536. Its totient is φ = 18077640.

The previous prime is 21090583. The next prime is 21090631. The reversal of 21090587 is 78509012.

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

It is not a de Polignac number, because 21090587 - 2² = 21090583 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21090583) by changing a digit.

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, 1506464 + ... + 1506477.

It is an arithmetic number, because the mean of its divisors is an integer number (6025884).

Almost surely, 2^21090587 is an apocalyptic number.

21090587 is a deficient number, since it is larger than the sum of its proper divisors (3012949).

21090587 is an equidigital number, since it uses as much as digits as its factorization.

21090587 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3012948.

The product of its (nonzero) digits is 5040, while the sum is 32.

The square root of 21090587 is about 4592.4489109842. The cubic root of 21090587 is about 276.2885512287.

Adding to 21090587 its reverse (78509012), we get a palindrome (99599599).

The spelling of 21090587 in words is "twenty-one million, ninety thousand, five hundred eighty-seven".