21090330 has 48 divisors (see below), whose sum is σ = 55472040. Its totient is φ = 5558784.

The previous prime is 21090299. The next prime is 21090341. The reversal of 21090330 is 3309012.

It can be written as a sum of positive squares in 4 ways, for example, as 9941409 + 11148921 = 3153^2 + 3339^2 .

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

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6694 + ... + 9326.

Almost surely, 2^21090330 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21090330, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27736020).

21090330 is an abundant number, since it is smaller than the sum of its proper divisors (34381710).

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

21090330 is a wasteful number, since it uses less digits than its factorization.

21090330 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2735 (or 2732 counting only the distinct ones).

The product of its (nonzero) digits is 162, while the sum is 18.

The square root of 21090330 is about 4592.4209301849. The cubic root of 21090330 is about 276.2874289833.

Adding to 21090330 its reverse (3309012), we get a palindrome (24399342).

The spelling of 21090330 in words is "twenty-one million, ninety thousand, three hundred thirty".