21258561 has 8 divisors (see below), whose sum is σ = 28809664. Its totient is φ = 13939920.

The previous prime is 21258547. The next prime is 21258563. The reversal of 21258561 is 16585212.

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

It is a de Polignac number, because none of the positive numbers 2^k-21258561 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21258563) 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, 57901 + ... + 58266.

It is an arithmetic number, because the mean of its divisors is an integer number (3601208).

Almost surely, 2^21258561 is an apocalyptic number.

It is an amenable number.

21258561 is a deficient number, since it is larger than the sum of its proper divisors (7551103).

21258561 is a wasteful number, since it uses less digits than its factorization.

21258561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 116231.

The product of its digits is 4800, while the sum is 30.

The square root of 21258561 is about 4610.7007059665. The cubic root of 21258561 is about 277.0201039334.

The spelling of 21258561 in words is "twenty-one million, two hundred fifty-eight thousand, five hundred sixty-one".