21561009 has 8 divisors (see below), whose sum is σ = 28836192. Its totient is φ = 14329920.

The previous prime is 21560989. The next prime is 21561011. The reversal of 21561009 is 90016512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21561009 - 2⁵ = 21560977 is a prime.

It is a Smith number, since the sum of its digits (24) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a self number, because there is not a number n which added to its sum of digits gives 21561009.

It is not an unprimeable number, because it can be changed into a prime (21560009) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9864 + ... + 11849.

It is an arithmetic number, because the mean of its divisors is an integer number (3604524).

Almost surely, 2^21561009 is an apocalyptic number.

It is an amenable number.

21561009 is a deficient number, since it is larger than the sum of its proper divisors (7275183).

21561009 is a wasteful number, since it uses less digits than its factorization.

21561009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22047.

The product of its (nonzero) digits is 540, while the sum is 24.

The square root of 21561009 is about 4643.3833569930. The cubic root of 21561009 is about 278.3276548337.

The spelling of 21561009 in words is "twenty-one million, five hundred sixty-one thousand, nine".