2391821 has 4 divisors (see below), whose sum is σ = 2394972. Its totient is φ = 2388672.

The previous prime is 2391799. The next prime is 2391827. The reversal of 2391821 is 1281932.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 662596 + 1729225 = 814^2 + 1315^2 .

It is a cyclic number.

It is not a de Polignac number, because 2391821 - 2¹⁰ = 2390797 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2391827) 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, 341 + ... + 2213.

It is an arithmetic number, because the mean of its divisors is an integer number (598743).

2^2391821 is an apocalyptic number.

It is an amenable number.

2391821 is a deficient number, since it is larger than the sum of its proper divisors (3151).

2391821 is a wasteful number, since it uses less digits than its factorization.

2391821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3150.

The product of its digits is 864, while the sum is 26.

The square root of 2391821 is about 1546.5513247222. The cubic root of 2391821 is about 133.7343254697.

The spelling of 2391821 in words is "two million, three hundred ninety-one thousand, eight hundred twenty-one".