21210390 has 64 divisors (see below), whose sum is σ = 59901120. Its totient is φ = 5322240.

The previous prime is 21210389. The next prime is 21210433. The reversal of 21210390 is 9301212.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 2280 + ... + 6900.

It is an arithmetic number, because the mean of its divisors is an integer number (935955).

Almost surely, 2^21210390 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21210390, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29950560).

21210390 is an abundant number, since it is smaller than the sum of its proper divisors (38690730).

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

21210390 is a wasteful number, since it uses less digits than its factorization.

21210390 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4654 (or 4648 counting only the distinct ones).

The product of its (nonzero) digits is 108, while the sum is 18.

The square root of 21210390 is about 4605.4739169818. The cubic root of 21210390 is about 276.8107070797.

The spelling of 21210390 in words is "twenty-one million, two hundred ten thousand, three hundred ninety".