21920009 has 4 divisors (see below), whose sum is σ = 22121220. Its totient is φ = 21718800.

The previous prime is 21919999. The next prime is 21920011. The reversal of 21920009 is 90002912.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7441984 + 14478025 = 2728^2 + 3805^2 .

It is a cyclic number.

It is not a de Polignac number, because 21920009 - 2⁸ = 21919753 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21920029) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 100442 + ... + 100659.

It is an arithmetic number, because the mean of its divisors is an integer number (5530305).

Almost surely, 2^21920009 is an apocalyptic number.

It is an amenable number.

21920009 is a deficient number, since it is larger than the sum of its proper divisors (201211).

21920009 is a wasteful number, since it uses less digits than its factorization.

21920009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 201210.

The product of its (nonzero) digits is 324, while the sum is 23.

The square root of 21920009 is about 4681.8809254401. The cubic root of 21920009 is about 279.8639177172.

The spelling of 21920009 in words is "twenty-one million, nine hundred twenty thousand, nine".