2165721157 has 4 divisors (see below), whose sum is σ = 2186747680. Its totient is φ = 2144694636.

The previous prime is 2165721133. The next prime is 2165721167. The reversal of 2165721157 is 7511275612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 2165721157 - 2¹¹ = 2165719109 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2165721127) 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, 10513107 + ... + 10513312.

It is an arithmetic number, because the mean of its divisors is an integer number (546686920).

Almost surely, 2^2165721157 is an apocalyptic number.

It is an amenable number.

2165721157 is a deficient number, since it is larger than the sum of its proper divisors (21026523).

2165721157 is a wasteful number, since it uses less digits than its factorization.

2165721157 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21026522.

The product of its digits is 29400, while the sum is 37.

The square root of 2165721157 is about 46537.3093012477. The cubic root of 2165721157 is about 1293.8010911172.

Adding to 2165721157 its reverse (7511275612), we get a palindrome (9676996769).

The spelling of 2165721157 in words is "two billion, one hundred sixty-five million, seven hundred twenty-one thousand, one hundred fifty-seven".