21820705 has 8 divisors (see below), whose sum is σ = 26318952. Its totient is φ = 17367168.

The previous prime is 21820703. The next prime is 21820709. The reversal of 21820705 is 50702812.

It can be written as a sum of positive squares in 4 ways, for example, as 2845969 + 18974736 = 1687^2 + 4356^2 .

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 21820705 - 2¹ = 21820703 is a prime.

It is a super-2 number, since 2×21820705² = 952286333394050, which contains 22 as substring.

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 21820705.

It is not an unprimeable number, because it can be changed into a prime (21820703) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10092 + ... + 12061.

It is an arithmetic number, because the mean of its divisors is an integer number (3289869).

Almost surely, 2^21820705 is an apocalyptic number.

It is an amenable number.

21820705 is a deficient number, since it is larger than the sum of its proper divisors (4498247).

21820705 is a wasteful number, since it uses less digits than its factorization.

21820705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22355.

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

The square root of 21820705 is about 4671.2637476383. The cubic root of 21820705 is about 279.4406563270.

The spelling of 21820705 in words is "twenty-one million, eight hundred twenty thousand, seven hundred five".