21210210 has 96 divisors (see below), whose sum is σ = 63752832. Its totient is φ = 4792320.

The previous prime is 21210197. The next prime is 21210221. The reversal of 21210210 is 1201212.

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

It is a junction number, because it is equal to n+sod(n) for n = 21210192 and 21210201.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 82402 + ... + 82658.

It is an arithmetic number, because the mean of its divisors is an integer number (664092).

Almost surely, 2^21210210 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21210210, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31876416).

21210210 is an abundant number, since it is smaller than the sum of its proper divisors (42542622).

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

21210210 is a wasteful number, since it uses less digits than its factorization.

21210210 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 408 (or 405 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 9.

The square root of 21210210 is about 4605.4543749776. The cubic root of 21210210 is about 276.8099240347.

Adding to 21210210 its reverse (1201212), we get a palindrome (22411422).

The spelling of 21210210 in words is "twenty-one million, two hundred ten thousand, two hundred ten".