21605207 has 4 divisors (see below), whose sum is σ = 23267160. Its totient is φ = 19943256.

The previous prime is 21605201. The next prime is 21605209. The reversal of 21605207 is 70250612.

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

It is a cyclic number.

It is not a de Polignac number, because 21605207 - 2⁴ = 21605191 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 (21605201) 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, 830957 + ... + 830982.

It is an arithmetic number, because the mean of its divisors is an integer number (5816790).

Almost surely, 2^21605207 is an apocalyptic number.

21605207 is a deficient number, since it is larger than the sum of its proper divisors (1661953).

21605207 is a wasteful number, since it uses less digits than its factorization.

21605207 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1661952.

The product of its (nonzero) digits is 840, while the sum is 23.

The square root of 21605207 is about 4648.1401657007. The cubic root of 21605207 is about 278.5177066938.

Adding to 21605207 its reverse (70250612), we get a palindrome (91855819).

It can be divided in two parts, 21605 and 207, that added together give a palindrome (21812).

The spelling of 21605207 in words is "twenty-one million, six hundred five thousand, two hundred seven".