21520403 has 4 divisors (see below), whose sum is σ = 21531120. Its totient is φ = 21509688.

The previous prime is 21520399. The next prime is 21520423. The reversal of 21520403 is 30402512.

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 is a cyclic number.

It is not a de Polignac number, because 21520403 - 2² = 21520399 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21520423) 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, 1343 + ... + 6696.

It is an arithmetic number, because the mean of its divisors is an integer number (5382780).

Almost surely, 2^21520403 is an apocalyptic number.

21520403 is a deficient number, since it is larger than the sum of its proper divisors (10717).

21520403 is an equidigital number, since it uses as much as digits as its factorization.

21520403 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10716.

The product of its (nonzero) digits is 240, while the sum is 17.

The square root of 21520403 is about 4639.0088381032. The cubic root of 21520403 is about 278.1528195545.

Adding to 21520403 its reverse (30402512), we get a palindrome (51922915).

The spelling of 21520403 in words is "twenty-one million, five hundred twenty thousand, four hundred three".