21210 has 32 divisors (see below), whose sum is σ = 58752. Its totient is φ = 4800.

The previous prime is 21193. The next prime is 21211. The reversal of 21210 is 1212.

It is a happy number.

21210 is an esthetic number in base 10, because in such base its adjacent digits differ by 1.

It is a Harshad number since it is a multiple of its sum of digits (6).

It is an alternating number because its digits alternate between even and odd.

It is a nialpdrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (21211) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 160 + ... + 260.

It is an arithmetic number, because the mean of its divisors is an integer number (1836).

2²¹²¹⁰ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21210, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29376).

21210 is an abundant number, since it is smaller than the sum of its proper divisors (37542).

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

21210 is a wasteful number, since it uses less digits than its factorization.

21210 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 118.

The product of its (nonzero) digits is 4, while the sum is 6.

The square root of 21210 is about 145.6365338780. The cubic root of 21210 is about 27.6809010477.

Adding to 21210 its reverse (1212), we get a palindrome (22422).

It can be divided in two parts, 212 and 10, that added together give a palindrome (222).

The spelling of 21210 in words is "twenty-one thousand, two hundred ten", and thus it is an iban number.