21817129 has 4 divisors (see below), whose sum is σ = 21842884. Its totient is φ = 21791376.

The previous prime is 21817123. The next prime is 21817141. The reversal of 21817129 is 92171812.

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 7033104 + 14784025 = 2652^2 + 3845^2 .

It is a cyclic number.

It is not a de Polignac number, because 21817129 - 2¹⁷ = 21686057 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 21817129.

It is not an unprimeable number, because it can be changed into a prime (21817123) 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, 11562 + ... + 13315.

It is an arithmetic number, because the mean of its divisors is an integer number (5460721).

Almost surely, 2^21817129 is an apocalyptic number.

It is an amenable number.

21817129 is a deficient number, since it is larger than the sum of its proper divisors (25755).

21817129 is an equidigital number, since it uses as much as digits as its factorization.

21817129 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25754.

The product of its digits is 2016, while the sum is 31.

The square root of 21817129 is about 4670.8809661562. The cubic root of 21817129 is about 279.4253904839.

The spelling of 21817129 in words is "twenty-one million, eight hundred seventeen thousand, one hundred twenty-nine".