21605943 has 4 divisors (see below), whose sum is σ = 28807928. Its totient is φ = 14403960.

The previous prime is 21605933. The next prime is 21605951. The reversal of 21605943 is 34950612.

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

It is not a de Polignac number, because 21605943 - 2⁵ = 21605911 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21605943.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21605923) 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, 3600988 + ... + 3600993.

It is an arithmetic number, because the mean of its divisors is an integer number (7201982).

Almost surely, 2^21605943 is an apocalyptic number.

21605943 is a deficient number, since it is larger than the sum of its proper divisors (7201985).

21605943 is an equidigital number, since it uses as much as digits as its factorization.

21605943 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7201984.

The product of its (nonzero) digits is 6480, while the sum is 30.

The square root of 21605943 is about 4648.2193364771. The cubic root of 21605943 is about 278.5208693065.

The spelling of 21605943 in words is "twenty-one million, six hundred five thousand, nine hundred forty-three".