21493891 has 4 divisors (see below), whose sum is σ = 22428432. Its totient is φ = 20559352.

The previous prime is 21493889. The next prime is 21493897. The reversal of 21493891 is 19839412.

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 21493891 - 2¹ = 21493889 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21493891.

It is not an unprimeable number, because it can be changed into a prime (21493897) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 467236 + ... + 467281.

It is an arithmetic number, because the mean of its divisors is an integer number (5607108).

Almost surely, 2^21493891 is an apocalyptic number.

21493891 is a deficient number, since it is larger than the sum of its proper divisors (934541).

21493891 is an equidigital number, since it uses as much as digits as its factorization.

21493891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 934540.

The product of its digits is 15552, while the sum is 37.

The square root of 21493891 is about 4636.1504505354. The cubic root of 21493891 is about 278.0385494219.

The spelling of 21493891 in words is "twenty-one million, four hundred ninety-three thousand, eight hundred ninety-one".