21520819 has 4 divisors (see below), whose sum is σ = 21543696. Its totient is φ = 21497944.

The previous prime is 21520799. The next prime is 21520831. The reversal of 21520819 is 91802512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21520819 - 2⁹ = 21520307 is a prime.

It is a super-2 number, since 2×21520819² = 926291300861522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21520879) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9964 + ... + 11929.

It is an arithmetic number, because the mean of its divisors is an integer number (5385924).

Almost surely, 2^21520819 is an apocalyptic number.

21520819 is a deficient number, since it is larger than the sum of its proper divisors (22877).

21520819 is an equidigital number, since it uses as much as digits as its factorization.

21520819 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22876.

The product of its (nonzero) digits is 1440, while the sum is 28.

The square root of 21520819 is about 4639.0536750505. The cubic root of 21520819 is about 278.1546118200.

The spelling of 21520819 in words is "twenty-one million, five hundred twenty thousand, eight hundred nineteen".