21280403 has 4 divisors (see below), whose sum is σ = 22014240. Its totient is φ = 20546568.

The previous prime is 21280393. The next prime is 21280409. The reversal of 21280403 is 30408212.

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 21280403 - 2⁴ = 21280387 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21280409) 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, 366875 + ... + 366932.

It is an arithmetic number, because the mean of its divisors is an integer number (5503560).

Almost surely, 2^21280403 is an apocalyptic number.

21280403 is a deficient number, since it is larger than the sum of its proper divisors (733837).

21280403 is an equidigital number, since it uses as much as digits as its factorization.

21280403 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 733836.

The product of its (nonzero) digits is 384, while the sum is 20.

The square root of 21280403 is about 4613.0687183262. The cubic root of 21280403 is about 277.1149457566.

Adding to 21280403 its reverse (30408212), we get a palindrome (51688615).

The spelling of 21280403 in words is "twenty-one million, two hundred eighty thousand, four hundred three".