21012891 has 4 divisors (see below), whose sum is σ = 28017192. Its totient is φ = 14008592.

The previous prime is 21012889. The next prime is 21012913. The reversal of 21012891 is 19821012.

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 21012891 - 2¹ = 21012889 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21012821) 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, 3502146 + ... + 3502151.

It is an arithmetic number, because the mean of its divisors is an integer number (7004298).

Almost surely, 2^21012891 is an apocalyptic number.

21012891 is a deficient number, since it is larger than the sum of its proper divisors (7004301).

21012891 is an equidigital number, since it uses as much as digits as its factorization.

21012891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7004300.

The product of its (nonzero) digits is 288, while the sum is 24.

The square root of 21012891 is about 4583.9820025825. The cubic root of 21012891 is about 275.9488589345.

The spelling of 21012891 in words is "twenty-one million, twelve thousand, eight hundred ninety-one".