21561853 has 4 divisors (see below), whose sum is σ = 21915388. Its totient is φ = 21208320.

The previous prime is 21561851. The next prime is 21561887. The reversal of 21561853 is 35816512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 521284 + 21040569 = 722^2 + 4587^2 .

It is a cyclic number.

It is not a de Polignac number, because 21561853 - 2¹ = 21561851 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21561851) 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, 176676 + ... + 176797.

It is an arithmetic number, because the mean of its divisors is an integer number (5478847).

Almost surely, 2^21561853 is an apocalyptic number.

It is an amenable number.

21561853 is a deficient number, since it is larger than the sum of its proper divisors (353535).

21561853 is an equidigital number, since it uses as much as digits as its factorization.

21561853 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 353534.

The product of its digits is 7200, while the sum is 31.

The square root of 21561853 is about 4643.4742381109. The cubic root of 21561853 is about 278.3312864738.

The spelling of 21561853 in words is "twenty-one million, five hundred sixty-one thousand, eight hundred fifty-three".