21605873 has 4 divisors (see below), whose sum is σ = 21633780. Its totient is φ = 21577968.

The previous prime is 21605867. The next prime is 21605879. The reversal of 21605873 is 37850612.

It is a happy number.

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

It is an interprime number because it is at equal distance from previous prime (21605867) and next prime (21605879).

It can be written as a sum of positive squares in 2 ways, for example, as 8479744 + 13126129 = 2912^2 + 3623^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21605873 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21605879) 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, 12758 + ... + 14351.

It is an arithmetic number, because the mean of its divisors is an integer number (5408445).

Almost surely, 2^21605873 is an apocalyptic number.

It is an amenable number.

21605873 is a deficient number, since it is larger than the sum of its proper divisors (27907).

21605873 is an equidigital number, since it uses as much as digits as its factorization.

21605873 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27906.

The product of its (nonzero) digits is 10080, while the sum is 32.

The square root of 21605873 is about 4648.2118067059. The cubic root of 21605873 is about 278.5205685176.

The spelling of 21605873 in words is "twenty-one million, six hundred five thousand, eight hundred seventy-three".