21990909 has 4 divisors (see below), whose sum is σ = 29321216. Its totient is φ = 14660604.

The previous prime is 21990907. The next prime is 21990949. The reversal of 21990909 is 90909912.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21990909 - 2¹ = 21990907 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21990907) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3665149 + ... + 3665154.

It is an arithmetic number, because the mean of its divisors is an integer number (7330304).

Almost surely, 2^21990909 is an apocalyptic number.

It is an amenable number.

21990909 is a deficient number, since it is larger than the sum of its proper divisors (7330307).

21990909 is an equidigital number, since it uses as much as digits as its factorization.

21990909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7330306.

The product of its (nonzero) digits is 13122, while the sum is 39.

The square root of 21990909 is about 4689.4465558315. The cubic root of 21990909 is about 280.1653317790.

The spelling of 21990909 in words is "twenty-one million, nine hundred ninety thousand, nine hundred nine".