21370821 has 4 divisors (see below), whose sum is σ = 28494432. Its totient is φ = 14247212.

The previous prime is 21370807. The next prime is 21370829. The reversal of 21370821 is 12807312.

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 not a de Polignac number, because 21370821 - 2⁷ = 21370693 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21370791 and 21370800.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21370829) 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, 3561801 + ... + 3561806.

It is an arithmetic number, because the mean of its divisors is an integer number (7123608).

Almost surely, 2^21370821 is an apocalyptic number.

It is an amenable number.

21370821 is a deficient number, since it is larger than the sum of its proper divisors (7123611).

21370821 is an equidigital number, since it uses as much as digits as its factorization.

21370821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7123610.

The product of its (nonzero) digits is 672, while the sum is 24.

The square root of 21370821 is about 4622.8585312553. The cubic root of 21370821 is about 277.5068677791.

The spelling of 21370821 in words is "twenty-one million, three hundred seventy thousand, eight hundred twenty-one".