21549409 has 16 divisors (see below), whose sum is σ = 25315840. Its totient is φ = 17962560.

The previous prime is 21549397. The next prime is 21549427. The reversal of 21549409 is 90494512.

It is not a de Polignac number, because 21549409 - 2⁹ = 21548897 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21549449) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 46312 + ... + 46774.

It is an arithmetic number, because the mean of its divisors is an integer number (1582240).

Almost surely, 2^21549409 is an apocalyptic number.

It is an amenable number.

21549409 is a deficient number, since it is larger than the sum of its proper divisors (3766431).

21549409 is a wasteful number, since it uses less digits than its factorization.

21549409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 640.

The product of its (nonzero) digits is 12960, while the sum is 34.

The square root of 21549409 is about 4642.1340997433. The cubic root of 21549409 is about 278.2777316912.

The spelling of 21549409 in words is "twenty-one million, five hundred forty-nine thousand, four hundred nine".