21087091 has 4 divisors (see below), whose sum is σ = 21109000. Its totient is φ = 21065184.

The previous prime is 21087061. The next prime is 21087133. The reversal of 21087091 is 19078012.

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 21087091 - 2⁷ = 21086963 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21087041) 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, 9441 + ... + 11458.

It is an arithmetic number, because the mean of its divisors is an integer number (5277250).

Almost surely, 2^21087091 is an apocalyptic number.

21087091 is a deficient number, since it is larger than the sum of its proper divisors (21909).

21087091 is a wasteful number, since it uses less digits than its factorization.

21087091 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21908.

The product of its (nonzero) digits is 1008, while the sum is 28.

The square root of 21087091 is about 4592.0682703984. The cubic root of 21087091 is about 276.2732844156.

The spelling of 21087091 in words is "twenty-one million, eighty-seven thousand, ninety-one".