21535805 has 4 divisors (see below), whose sum is σ = 25842972. Its totient is φ = 17228640.

The previous prime is 21535781. The next prime is 21535837. The reversal of 21535805 is 50853512.

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 5583769 + 15952036 = 2363^2 + 3994^2 .

It is not a de Polignac number, because 21535805 - 2¹² = 21531709 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2153576 + ... + 2153585.

It is an arithmetic number, because the mean of its divisors is an integer number (6460743).

Almost surely, 2^21535805 is an apocalyptic number.

It is an amenable number.

21535805 is a deficient number, since it is larger than the sum of its proper divisors (4307167).

21535805 is an equidigital number, since it uses as much as digits as its factorization.

21535805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4307166.

The product of its (nonzero) digits is 6000, while the sum is 29.

The square root of 21535805 is about 4640.6685940713. The cubic root of 21535805 is about 278.2191610646.

The spelling of 21535805 in words is "twenty-one million, five hundred thirty-five thousand, eight hundred five".