21397129 has 4 divisors (see below), whose sum is σ = 23043076. Its totient is φ = 19751184.

The previous prime is 21397093. The next prime is 21397139. The reversal of 21397129 is 92179312.

It is a happy number.

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 8111104 + 13286025 = 2848^2 + 3645^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21397129 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21397094 and 21397103.

It is not an unprimeable number, because it can be changed into a prime (21397139) 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, 822954 + ... + 822979.

It is an arithmetic number, because the mean of its divisors is an integer number (5760769).

Almost surely, 2^21397129 is an apocalyptic number.

It is an amenable number.

21397129 is a deficient number, since it is larger than the sum of its proper divisors (1645947).

21397129 is a wasteful number, since it uses less digits than its factorization.

21397129 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1645946.

The product of its digits is 6804, while the sum is 34.

The square root of 21397129 is about 4625.7030816947. The cubic root of 21397129 is about 277.6206936504.

The spelling of 21397129 in words is "twenty-one million, three hundred ninety-seven thousand, one hundred twenty-nine".