21806605 has 8 divisors (see below), whose sum is σ = 26203032. Its totient is φ = 17421888.

The previous prime is 21806593. The next prime is 21806621. The reversal of 21806605 is 50660812.

It can be written as a sum of positive squares in 4 ways, for example, as 6666724 + 15139881 = 2582^2 + 3891^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21806605 - 2⁵ = 21806573 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1899 + ... + 6871.

It is an arithmetic number, because the mean of its divisors is an integer number (3275379).

Almost surely, 2^21806605 is an apocalyptic number.

It is an amenable number.

21806605 is a deficient number, since it is larger than the sum of its proper divisors (4396427).

21806605 is an equidigital number, since it uses as much as digits as its factorization.

21806605 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5855.

The product of its (nonzero) digits is 2880, while the sum is 28.

The square root of 21806605 is about 4669.7542761906. The cubic root of 21806605 is about 279.3804541440.

The spelling of 21806605 in words is "twenty-one million, eight hundred six thousand, six hundred five".