21331087 has 4 divisors (see below), whose sum is σ = 21375376. Its totient is φ = 21286800.

The previous prime is 21331081. The next prime is 21331103. The reversal of 21331087 is 78013312.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21331087 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21331081) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21414 + ... + 22387.

It is an arithmetic number, because the mean of its divisors is an integer number (5343844).

Almost surely, 2^21331087 is an apocalyptic number.

21331087 is a deficient number, since it is larger than the sum of its proper divisors (44289).

21331087 is an equidigital number, since it uses as much as digits as its factorization.

21331087 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 44288.

The product of its (nonzero) digits is 1008, while the sum is 25.

The square root of 21331087 is about 4618.5589743988. The cubic root of 21331087 is about 277.3347748952.

Adding to 21331087 its reverse (78013312), we get a palindrome (99344399).

The spelling of 21331087 in words is "twenty-one million, three hundred thirty-one thousand, eighty-seven".