21400 has 24 divisors (see below), whose sum is σ = 50220. Its totient is φ = 8480.

The previous prime is 21397. The next prime is 21401. The reversal of 21400 is 412.

It is a nialpdrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21401) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 147 + ... + 253.

2²¹⁴⁰⁰ is an apocalyptic number.

21400 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25110).

21400 is an abundant number, since it is smaller than the sum of its proper divisors (28820).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21400 is a wasteful number, since it uses less digits than its factorization.

21400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 123 (or 114 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 7.

The square root of 21400 is about 146.2873883833. The cubic root of 21400 is about 27.7633109855.

Adding to 21400 its reverse (412), we get a palindrome (21812).

The spelling of 21400 in words is "twenty-one thousand, four hundred", and thus it is an iban number.