2165724021 has 4 divisors (see below), whose sum is σ = 2887632032. Its totient is φ = 1443816012.

The previous prime is 2165724019. The next prime is 2165724023. The reversal of 2165724021 is 1204275612.

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 an interprime number because it is at equal distance from previous prime (2165724019) and next prime (2165724023).

It is not a de Polignac number, because 2165724021 - 2¹ = 2165724019 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 2165724021.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2165724023) 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, 360954001 + ... + 360954006.

It is an arithmetic number, because the mean of its divisors is an integer number (721908008).

Almost surely, 2^2165724021 is an apocalyptic number.

It is an amenable number.

2165724021 is a deficient number, since it is larger than the sum of its proper divisors (721908011).

2165724021 is an equidigital number, since it uses as much as digits as its factorization.

2165724021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 721908010.

The product of its (nonzero) digits is 6720, while the sum is 30.

The square root of 2165724021 is about 46537.3400722474. The cubic root of 2165724021 is about 1293.8016614344.

Adding to 2165724021 its reverse (1204275612), we get a palindrome (3369999633).

The spelling of 2165724021 in words is "two billion, one hundred sixty-five million, seven hundred twenty-four thousand, twenty-one".