21820129 has 4 divisors (see below), whose sum is σ = 23103684. Its totient is φ = 20536576.

The previous prime is 21820111. The next prime is 21820133. The reversal of 21820129 is 92102812.

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

It can be written as a sum of positive squares in 2 ways, for example, as 18662400 + 3157729 = 4320^2 + 1777^2 .

It is a cyclic number.

It is not a de Polignac number, because 21820129 - 2²³ = 13431521 is a prime.

It is a super-2 number, since 2×21820129² = 952236059153282, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21820429) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 641752 + ... + 641785.

It is an arithmetic number, because the mean of its divisors is an integer number (5775921).

Almost surely, 2^21820129 is an apocalyptic number.

It is an amenable number.

21820129 is a deficient number, since it is larger than the sum of its proper divisors (1283555).

21820129 is a wasteful number, since it uses less digits than its factorization.

21820129 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1283554.

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 21820129 is about 4671.2020936800. The cubic root of 21820129 is about 279.4381975119.

The spelling of 21820129 in words is "twenty-one million, eight hundred twenty thousand, one hundred twenty-nine".