21129259 has 4 divisors (see below), whose sum is σ = 21810880. Its totient is φ = 20447640.

The previous prime is 21129239. The next prime is 21129263. The reversal of 21129259 is 95292112.

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

It is a cyclic number.

It is not a de Polignac number, because 21129259 - 2⁷ = 21129131 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31), and also a Moran number because the ratio is a prime number: 681589 = 21129259 / (2 + 1 + 1 + 2 + 9 + 2 + 5 + 9).

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 21129259.

It is not an unprimeable number, because it can be changed into a prime (21129209) 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, 340764 + ... + 340825.

It is an arithmetic number, because the mean of its divisors is an integer number (5452720).

Almost surely, 2^21129259 is an apocalyptic number.

21129259 is a deficient number, since it is larger than the sum of its proper divisors (681621).

21129259 is an equidigital number, since it uses as much as digits as its factorization.

21129259 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 681620.

The product of its digits is 3240, while the sum is 31.

The square root of 21129259 is about 4596.6573724827. The cubic root of 21129259 is about 276.4573169914.

The spelling of 21129259 in words is "twenty-one million, one hundred twenty-nine thousand, two hundred fifty-nine".