Adding to 21403 its reverse (30412), we get a palindrome (51815).
Subtracting 21403 from its reverse (30412), we obtain a palindrome (9009).
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 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.
221403 is an apocalyptic number.
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 square root of 21403 is about 146.2976418128. The cubic root of 21403 is about 27.7646082758.
The spelling of 21403 in words is "twenty-one thousand, four hundred three", and thus it is an iban number.