2157691 has 4 divisors (see below), whose sum is σ = 2284632. Its totient is φ = 2030752.

The previous prime is 2157679. The next prime is 2157709. The reversal of 2157691 is 1967512.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 2157691 - 2⁷ = 2157563 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2157641) 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, 63445 + ... + 63478.

It is an arithmetic number, because the mean of its divisors is an integer number (571158).

2^2157691 is an apocalyptic number.

2157691 is a deficient number, since it is larger than the sum of its proper divisors (126941).

2157691 is a wasteful number, since it uses less digits than its factorization.

2157691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 126940.

The product of its digits is 3780, while the sum is 31.

The square root of 2157691 is about 1468.9080978741. The cubic root of 2157691 is about 129.2200039636.

The spelling of 2157691 in words is "two million, one hundred fifty-seven thousand, six hundred ninety-one".