2185721 has 4 divisors (see below), whose sum is σ = 2188944. Its totient is φ = 2182500.

The previous prime is 2185709. The next prime is 2185723. The reversal of 2185721 is 1275812.

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 2185721 - 2⁶ = 2185657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2185723) 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, 155 + ... + 2096.

It is an arithmetic number, because the mean of its divisors is an integer number (547236).

2^2185721 is an apocalyptic number.

It is an amenable number.

2185721 is a deficient number, since it is larger than the sum of its proper divisors (3223).

2185721 is an equidigital number, since it uses as much as digits as its factorization.

2185721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3222.

The product of its digits is 1120, while the sum is 26.

The square root of 2185721 is about 1478.4184116819. The cubic root of 2185721 is about 129.7771527281. Note that the first 3 decimals are identical.

Subtracting from 2185721 its reverse (1275812), we obtain a palindrome (909909).

The spelling of 2185721 in words is "two million, one hundred eighty-five thousand, seven hundred twenty-one".