21123210 has 64 divisors (see below), whose sum is σ = 52752384. Its totient is φ = 5409600.

The previous prime is 21123187. The next prime is 21123211. The reversal of 21123210 is 1232112.

It is not an unprimeable number, because it can be changed into a prime (21123211) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 100005 + ... + 100215.

It is an arithmetic number, because the mean of its divisors is an integer number (824256).

Almost surely, 2^21123210 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21123210, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26376192).

21123210 is an abundant number, since it is smaller than the sum of its proper divisors (31629174).

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

21123210 is a wasteful number, since it uses less digits than its factorization.

21123210 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 339.

The product of its (nonzero) digits is 24, while the sum is 12.

The square root of 21123210 is about 4595.9993472584. Note that the first 3 decimals coincide. The cubic root of 21123210 is about 276.4309325684.

Adding to 21123210 its reverse (1232112), we get a palindrome (22355322).

The spelling of 21123210 in words is "twenty-one million, one hundred twenty-three thousand, two hundred ten".