21390841 has 4 divisors (see below), whose sum is σ = 21402000. Its totient is φ = 21379684.

The previous prime is 21390833. The next prime is 21390857. The reversal of 21390841 is 14809312.

It is a happy number.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21390841 - 2³ = 21390833 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21390871) 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, 1891 + ... + 6808.

It is an arithmetic number, because the mean of its divisors is an integer number (5350500).

Almost surely, 2^21390841 is an apocalyptic number.

It is an amenable number.

21390841 is a deficient number, since it is larger than the sum of its proper divisors (11159).

21390841 is an equidigital number, since it uses as much as digits as its factorization.

21390841 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11158.

The product of its (nonzero) digits is 1728, while the sum is 28.

The square root of 21390841 is about 4625.0233512924. The cubic root of 21390841 is about 277.5934960771.

The spelling of 21390841 in words is "twenty-one million, three hundred ninety thousand, eight hundred forty-one".