21129715 has 4 divisors (see below), whose sum is σ = 25355664. Its totient is φ = 16903768.

The previous prime is 21129707. The next prime is 21129737. The reversal of 21129715 is 51792112.

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 21129715 - 2³ = 21129707 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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, 2112967 + ... + 2112976.

It is an arithmetic number, because the mean of its divisors is an integer number (6338916).

Almost surely, 2^21129715 is an apocalyptic number.

21129715 is a deficient number, since it is larger than the sum of its proper divisors (4225949).

21129715 is an equidigital number, since it uses as much as digits as its factorization.

21129715 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4225948.

The product of its digits is 1260, while the sum is 28.

The square root of 21129715 is about 4596.7069734757. The cubic root of 21129715 is about 276.4593057601.

The spelling of 21129715 in words is "twenty-one million, one hundred twenty-nine thousand, seven hundred fifteen".