21072891 has 16 divisors (see below), whose sum is σ = 32768000. Its totient is φ = 12041064.

The previous prime is 21072889. The next prime is 21072923. The reversal of 21072891 is 19827012.

It is not a de Polignac number, because 21072891 - 2¹ = 21072889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21072841) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9211 + ... + 11268.

It is an arithmetic number, because the mean of its divisors is an integer number (2048000).

Almost surely, 2^21072891 is an apocalyptic number.

21072891 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21072891 is a deficient number, since it is larger than the sum of its proper divisors (11695109).

21072891 is an equidigital number, since it uses as much as digits as its factorization.

21072891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20503 (or 20489 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 30.

The square root of 21072891 is about 4590.5218657577. The cubic root of 21072891 is about 276.2112565527.

The spelling of 21072891 in words is "twenty-one million, seventy-two thousand, eight hundred ninety-one".