21420 has 72 divisors (see below), whose sum is σ = 78624. Its totient is φ = 4608.

The previous prime is 21419. The next prime is 21433. The reversal of 21420 is 2412.

21420 = T₁₆ + T₁₇ + ... + T₅₀.

21420 is nontrivially palindromic in base 13.

21420 is digitally balanced in base 4, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (9).

21420 is a nontrivial repdigit in base 13.

It is a plaindrome in base 13.

It is a nialpdrome in base 13 and base 15.

It is a zygodrome in base 13.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1252 + ... + 1268.

It is an arithmetic number, because the mean of its divisors is an integer number (1092).

2²¹⁴²⁰ is an apocalyptic number.

21420 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 21420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39312).

21420 is an abundant number, since it is smaller than the sum of its proper divisors (57204).

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

21420 is a wasteful number, since it uses less digits than its factorization.

21420 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39 (or 34 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 9.

The square root of 21420 is about 146.3557310118. The cubic root of 21420 is about 27.7719572990.

Adding to 21420 its reverse (2412), we get a palindrome (23832).

It can be divided in two parts, 21 and 420, that added together give a square (441 = 21²).

The spelling of 21420 in words is "twenty-one thousand, four hundred twenty", and thus it is an iban number.