21757891 has 4 divisors (see below), whose sum is σ = 21767392. Its totient is φ = 21748392.

The previous prime is 21757873. The next prime is 21757951. The reversal of 21757891 is 19875712.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21757891 - 2¹¹ = 21755843 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21757091) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1030 + ... + 6676.

It is an arithmetic number, because the mean of its divisors is an integer number (5441848).

Almost surely, 2^21757891 is an apocalyptic number.

21757891 is a deficient number, since it is larger than the sum of its proper divisors (9501).

21757891 is an equidigital number, since it uses as much as digits as its factorization.

21757891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9500.

The product of its digits is 35280, while the sum is 40.

The square root of 21757891 is about 4664.5354538260. The cubic root of 21757891 is about 279.1722620794.

The spelling of 21757891 in words is "twenty-one million, seven hundred fifty-seven thousand, eight hundred ninety-one".