21597409 has 4 divisors (see below), whose sum is σ = 21610516. Its totient is φ = 21584304.

The previous prime is 21597377. The next prime is 21597427. The reversal of 21597409 is 90479512.

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 12446784 + 9150625 = 3528^2 + 3025^2 .

It is a cyclic number.

It is not a de Polignac number, because 21597409 - 2⁵ = 21597377 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21597449) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3654 + ... + 7519.

It is an arithmetic number, because the mean of its divisors is an integer number (5402629).

Almost surely, 2^21597409 is an apocalyptic number.

It is an amenable number.

21597409 is a deficient number, since it is larger than the sum of its proper divisors (13107).

21597409 is a wasteful number, since it uses less digits than its factorization.

21597409 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13106.

The product of its (nonzero) digits is 22680, while the sum is 37.

The square root of 21597409 is about 4647.3012598712. The cubic root of 21597409 is about 278.4841940561.

The spelling of 21597409 in words is "twenty-one million, five hundred ninety-seven thousand, four hundred nine".