21207805 has 8 divisors (see below), whose sum is σ = 25582392. Its totient is φ = 16877568.

The previous prime is 21207793. The next prime is 21207811. The reversal of 21207805 is 50870212.

It can be written as a sum of positive squares in 4 ways, for example, as 605284 + 20602521 = 778^2 + 4539^2 .

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 21207805 - 2⁵ = 21207773 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 21207805.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10024 + ... + 11953.

It is an arithmetic number, because the mean of its divisors is an integer number (3197799).

Almost surely, 2^21207805 is an apocalyptic number.

It is an amenable number.

21207805 is a deficient number, since it is larger than the sum of its proper divisors (4374587).

21207805 is a wasteful number, since it uses less digits than its factorization.

21207805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22175.

The product of its (nonzero) digits is 1120, while the sum is 25.

The square root of 21207805 is about 4605.1932641313. The cubic root of 21207805 is about 276.7994612587.

The spelling of 21207805 in words is "twenty-one million, two hundred seven thousand, eight hundred five".