21384409 has 4 divisors (see below), whose sum is σ = 21962404. Its totient is φ = 20806416.

The previous prime is 21384403. The next prime is 21384413. The reversal of 21384409 is 90448312.

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 7546009 + 13838400 = 2747^2 + 3720^2 .

It is a cyclic number.

It is not a de Polignac number, because 21384409 - 2¹³ = 21376217 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21384403) 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, 288942 + ... + 289015.

It is an arithmetic number, because the mean of its divisors is an integer number (5490601).

Almost surely, 2^21384409 is an apocalyptic number.

It is an amenable number.

21384409 is a deficient number, since it is larger than the sum of its proper divisors (577995).

21384409 is an equidigital number, since it uses as much as digits as its factorization.

21384409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 577994.

The product of its (nonzero) digits is 6912, while the sum is 31.

The square root of 21384409 is about 4624.3279511730. The cubic root of 21384409 is about 277.5656701437.

The spelling of 21384409 in words is "twenty-one million, three hundred eighty-four thousand, four hundred nine".