21840401 has 4 divisors (see below), whose sum is σ = 23825904. Its totient is φ = 19854900.

The previous prime is 21840391. The next prime is 21840407. The reversal of 21840401 is 10404812.

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 a de Polignac number, because none of the positive numbers 2^k-21840401 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21840407) 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, 992735 + ... + 992756.

It is an arithmetic number, because the mean of its divisors is an integer number (5956476).

Almost surely, 2^21840401 is an apocalyptic number.

It is an amenable number.

21840401 is a deficient number, since it is larger than the sum of its proper divisors (1985503).

21840401 is a wasteful number, since it uses less digits than its factorization.

21840401 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1985502.

The product of its (nonzero) digits is 256, while the sum is 20.

The square root of 21840401 is about 4673.3714810616. The cubic root of 21840401 is about 279.5247081181.

The spelling of 21840401 in words is "twenty-one million, eight hundred forty thousand, four hundred one".