2157891 has 4 divisors (see below), whose sum is σ = 2877192. Its totient is φ = 1438592.

The previous prime is 2157863. The next prime is 2157893. The reversal of 2157891 is 1987512.

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 2157891 - 2⁷ = 2157763 is a prime.

It is an Ulam number.

It is a D-number.

It is not an unprimeable number, because it can be changed into a prime (2157893) 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, 359646 + ... + 359651.

It is an arithmetic number, because the mean of its divisors is an integer number (719298).

2^2157891 is an apocalyptic number.

2157891 is a deficient number, since it is larger than the sum of its proper divisors (719301).

2157891 is an equidigital number, since it uses as much as digits as its factorization.

2157891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 719300.

The product of its digits is 5040, while the sum is 33.

The square root of 2157891 is about 1468.9761740750. The cubic root of 2157891 is about 129.2239963800.

The spelling of 2157891 in words is "two million, one hundred fifty-seven thousand, eight hundred ninety-one".