21405210 has 96 divisors (see below), whose sum is σ = 58501440. Its totient is φ = 4981248.

The previous prime is 21405187. The next prime is 21405247. The reversal of 21405210 is 1250412.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21405210.

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, 455407 + ... + 455453.

It is an arithmetic number, because the mean of its divisors is an integer number (609390).

Almost surely, 2^21405210 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21405210, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29250720).

21405210 is an abundant number, since it is smaller than the sum of its proper divisors (37096230).

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

21405210 is a wasteful number, since it uses less digits than its factorization.

21405210 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 140 (or 93 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 15.

The square root of 21405210 is about 4626.5764880741. The cubic root of 21405210 is about 277.6556386884.

Adding to 21405210 its reverse (1250412), we get a palindrome (22655622).

The spelling of 21405210 in words is "twenty-one million, four hundred five thousand, two hundred ten".