2188721 has 4 divisors (see below), whose sum is σ = 2193444. Its totient is φ = 2184000.

The previous prime is 2188691. The next prime is 2188729. The reversal of 2188721 is 1278812.

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

It can be written as a sum of positive squares in 2 ways, for example, as 336400 + 1852321 = 580^2 + 1361^2 .

It is a cyclic number.

It is not a de Polignac number, because 2188721 - 2¹⁰ = 2187697 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2188729) 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, 1580 + ... + 2621.

It is an arithmetic number, because the mean of its divisors is an integer number (548361).

2^2188721 is an apocalyptic number.

It is an amenable number.

2188721 is a deficient number, since it is larger than the sum of its proper divisors (4723).

2188721 is an equidigital number, since it uses as much as digits as its factorization.

2188721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4722.

The product of its digits is 1792, while the sum is 29.

The square root of 2188721 is about 1479.4326615294. The cubic root of 2188721 is about 129.8365005693.

Subtracting from 2188721 its reverse (1278812), we obtain a palindrome (909909).

The spelling of 2188721 in words is "two million, one hundred eighty-eight thousand, seven hundred twenty-one".