21090390 has 16 divisors (see below), whose sum is σ = 50617008. Its totient is φ = 5624096.

The previous prime is 21090373. The next prime is 21090397. The reversal of 21090390 is 9309012.

It is a happy number.

It is a Smith number, since the sum of its digits (24) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a self number, because there is not a number n which added to its sum of digits gives 21090390.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21090397) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 351477 + ... + 351536.

It is an arithmetic number, because the mean of its divisors is an integer number (3163563).

Almost surely, 2^21090390 is an apocalyptic number.

21090390 is an abundant number, since it is smaller than the sum of its proper divisors (29526618).

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

21090390 is a wasteful number, since it uses less digits than its factorization.

21090390 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 703023.

The product of its (nonzero) digits is 486, while the sum is 24.

The square root of 21090390 is about 4592.4274626825. The cubic root of 21090390 is about 276.2876909869.

The spelling of 21090390 in words is "twenty-one million, ninety thousand, three hundred ninety".