2191921 has 4 divisors (see below), whose sum is σ = 2233332. Its totient is φ = 2150512.

The previous prime is 2191883. The next prime is 2191949. The reversal of 2191921 is 1291912.

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 1527696 + 664225 = 1236^2 + 815^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2191921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2191951) 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, 20626 + ... + 20731.

It is an arithmetic number, because the mean of its divisors is an integer number (558333).

2^2191921 is an apocalyptic number.

It is an amenable number.

2191921 is a deficient number, since it is larger than the sum of its proper divisors (41411).

2191921 is an equidigital number, since it uses as much as digits as its factorization.

2191921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41410.

The product of its digits is 324, while the sum is 25.

The square root of 2191921 is about 1480.5137621785. The cubic root of 2191921 is about 129.8997451895.

Subtracting from 2191921 its reverse (1291912), we obtain a palindrome (900009).

The spelling of 2191921 in words is "two million, one hundred ninety-one thousand, nine hundred twenty-one".