21820729 has 6 divisors (see below), whose sum is σ = 25383354. Its totient is φ = 18703440.

The previous prime is 21820709. The next prime is 21820751. The reversal of 21820729 is 92702812.

It can be written as a sum of positive squares in only one way, i.e., 20070400 + 1750329 = 4480^2 + 1323^2 .

It is not a de Polignac number, because 21820729 - 2⁵ = 21820697 is a prime.

It is a super-2 number, since 2×21820729² = 952288428182882, 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 21820729.

It is not an unprimeable number, because it can be changed into a prime (21820709) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 222612 + ... + 222709.

It is an arithmetic number, because the mean of its divisors is an integer number (4230559).

Almost surely, 2^21820729 is an apocalyptic number.

It is an amenable number.

21820729 is a deficient number, since it is larger than the sum of its proper divisors (3562625).

21820729 is an equidigital number, since it uses as much as digits as its factorization.

21820729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 445335 (or 445328 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 21820729 is about 4671.2663165356. The cubic root of 21820729 is about 279.4407587767.

The spelling of 21820729 in words is "twenty-one million, eight hundred twenty thousand, seven hundred twenty-nine".