21729879 has 12 divisors (see below), whose sum is σ = 31554432. Its totient is φ = 14409600.

The previous prime is 21729821. The next prime is 21729889. The reversal of 21729879 is 97892712.

It is not a de Polignac number, because 21729879 - 2⁷ = 21729751 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21729889) 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 11 ways as a sum of consecutive naturals, for example, 4602 + ... + 8039.

It is an arithmetic number, because the mean of its divisors is an integer number (2629536).

Almost surely, 2^21729879 is an apocalyptic number.

21729879 is a deficient number, since it is larger than the sum of its proper divisors (9824553).

21729879 is a wasteful number, since it uses less digits than its factorization.

21729879 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12838 (or 12835 counting only the distinct ones).

The product of its digits is 127008, while the sum is 45.

The square root of 21729879 is about 4661.5318297744. The cubic root of 21729879 is about 279.0524046935.

The spelling of 21729879 in words is "twenty-one million, seven hundred twenty-nine thousand, eight hundred seventy-nine".