21129401 has 4 divisors (see below), whose sum is σ = 21366900. Its totient is φ = 20891904.

The previous prime is 21129379. The next prime is 21129403. The reversal of 21129401 is 10492112.

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 4515625 + 16613776 = 2125^2 + 4076^2 .

It is a cyclic number.

It is not a de Polignac number, because 21129401 - 2⁶ = 21129337 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21129403) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 118616 + ... + 118793.

It is an arithmetic number, because the mean of its divisors is an integer number (5341725).

Almost surely, 2^21129401 is an apocalyptic number.

It is an amenable number.

21129401 is a deficient number, since it is larger than the sum of its proper divisors (237499).

21129401 is an equidigital number, since it uses as much as digits as its factorization.

21129401 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 237498.

The product of its (nonzero) digits is 144, while the sum is 20.

The square root of 21129401 is about 4596.6728184634. The cubic root of 21129401 is about 276.4579363040.

The spelling of 21129401 in words is "twenty-one million, one hundred twenty-nine thousand, four hundred one".