21218807 has 4 divisors (see below), whose sum is σ = 21950520. Its totient is φ = 20487096.

The previous prime is 21218777. The next prime is 21218809. The reversal of 21218807 is 70881212.

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 21218807 - 2⁸ = 21218551 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (29), and also a Moran number because the ratio is a prime number: 731683 = 21218807 / (2 + 1 + 2 + 1 + 8 + 8 + 0 + 7).

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 21218807.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21218809) 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, 365813 + ... + 365870.

It is an arithmetic number, because the mean of its divisors is an integer number (5487630).

Almost surely, 2^21218807 is an apocalyptic number.

21218807 is a deficient number, since it is larger than the sum of its proper divisors (731713).

21218807 is an equidigital number, since it uses as much as digits as its factorization.

21218807 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 731712.

The product of its (nonzero) digits is 1792, while the sum is 29.

The square root of 21218807 is about 4606.3876302370. The cubic root of 21218807 is about 276.8473181870.

The spelling of 21218807 in words is "twenty-one million, two hundred eighteen thousand, eight hundred seven".