21573009 has 6 divisors (see below), whose sum is σ = 31161026. Its totient is φ = 14382000.

The previous prime is 21572989. The next prime is 21573023. The reversal of 21573009 is 90037512.

It can be written as a sum of positive squares in only one way, i.e., 18948609 + 2624400 = 4353^2 + 1620^2 .

It is not a de Polignac number, because 21573009 - 2⁸ = 21572753 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21573029) 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 5 ways as a sum of consecutive naturals, for example, 1198492 + ... + 1198509.

Almost surely, 2^21573009 is an apocalyptic number.

It is an amenable number.

21573009 is a deficient number, since it is larger than the sum of its proper divisors (9588017).

21573009 is a wasteful number, since it uses less digits than its factorization.

21573009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2397007 (or 2397004 counting only the distinct ones).

The product of its (nonzero) digits is 1890, while the sum is 27.

The square root of 21573009 is about 4644.6753384925. The cubic root of 21573009 is about 278.3792806246.

The spelling of 21573009 in words is "twenty-one million, five hundred seventy-three thousand, nine".