21564561 has 8 divisors (see below), whose sum is σ = 29680384. Its totient is φ = 13912560.

The previous prime is 21564533. The next prime is 21564583. The reversal of 21564561 is 16546512.

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

It is not a de Polignac number, because 21564561 - 2⁶ = 21564497 is a prime.

It is a super-2 number, since 2×21564561² = 930060582245442, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21564511) 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, 115846 + ... + 116031.

It is an arithmetic number, because the mean of its divisors is an integer number (3710048).

Almost surely, 2^21564561 is an apocalyptic number.

It is an amenable number.

21564561 is a deficient number, since it is larger than the sum of its proper divisors (8115823).

21564561 is a wasteful number, since it uses less digits than its factorization.

21564561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 231911.

The product of its digits is 7200, while the sum is 30.

The square root of 21564561 is about 4643.7658209690. The cubic root of 21564561 is about 278.3429380632.

The spelling of 21564561 in words is "twenty-one million, five hundred sixty-four thousand, five hundred sixty-one".