21403 has 4 divisors (see below), whose sum is σ = 22680. Its totient is φ = 20128.

The previous prime is 21401. The next prime is 21407. The reversal of 21403 is 30412.

21403 is an esthetic number in base 9, because in such base its adjacent digits differ by 1.

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

It is not a de Polignac number, because 21403 - 2¹ = 21401 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 13.

It is a self number, because there is not a number n which added to its sum of digits gives 21403.

It is not an unprimeable number, because it can be changed into a prime (21401) 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, 613 + ... + 646.

It is an arithmetic number, because the mean of its divisors is an integer number (5670).

2²¹⁴⁰³ is an apocalyptic number.

21403 is a deficient number, since it is larger than the sum of its proper divisors (1277).

21403 is a wasteful number, since it uses less digits than its factorization.

21403 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1276.

The product of its (nonzero) digits is 24, while the sum is 10.

The square root of 21403 is about 146.2976418128. The cubic root of 21403 is about 27.7646082758.

Adding to 21403 its reverse (30412), we get a palindrome (51815).

Subtracting 21403 from its reverse (30412), we obtain a palindrome (9009).

It can be divided in two parts, 21 and 403, that added together give a palindrome (424).

The spelling of 21403 in words is "twenty-one thousand, four hundred three", and thus it is an iban number.