21078129 has 4 divisors (see below), whose sum is σ = 28104176. Its totient is φ = 14052084.

The previous prime is 21078121. The next prime is 21078131. The reversal of 21078129 is 92187012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21078129 - 2³ = 21078121 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21078096 and 21078105.

It is not an unprimeable number, because it can be changed into a prime (21078121) 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, 3513019 + ... + 3513024.

It is an arithmetic number, because the mean of its divisors is an integer number (7026044).

Almost surely, 2^21078129 is an apocalyptic number.

It is an amenable number.

21078129 is a deficient number, since it is larger than the sum of its proper divisors (7026047).

21078129 is an equidigital number, since it uses as much as digits as its factorization.

21078129 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7026046.

The product of its (nonzero) digits is 2016, while the sum is 30.

The square root of 21078129 is about 4591.0923536779. The cubic root of 21078129 is about 276.2341402141.

The spelling of 21078129 in words is "twenty-one million, seventy-eight thousand, one hundred twenty-nine".