21852561 has 4 divisors (see below), whose sum is σ = 29136752. Its totient is φ = 14568372.

The previous prime is 21852547. The next prime is 21852587. The reversal of 21852561 is 16525812.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21852561 - 2⁵ = 21852529 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 (21852511) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3642091 + ... + 3642096.

It is an arithmetic number, because the mean of its divisors is an integer number (7284188).

Almost surely, 2^21852561 is an apocalyptic number.

It is an amenable number.

21852561 is a deficient number, since it is larger than the sum of its proper divisors (7284191).

21852561 is an equidigital number, since it uses as much as digits as its factorization.

21852561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7284190.

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

The square root of 21852561 is about 4674.6722879791. The cubic root of 21852561 is about 279.5765751424.

The spelling of 21852561 in words is "twenty-one million, eight hundred fifty-two thousand, five hundred sixty-one".