21645879 has 8 divisors (see below), whose sum is σ = 30558960. Its totient is φ = 13581696.

The previous prime is 21645859. The next prime is 21645881. The reversal of 21645879 is 97854612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21645879 - 2⁷ = 21645751 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21645879.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21645809) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 212164 + ... + 212265.

It is an arithmetic number, because the mean of its divisors is an integer number (3819870).

Almost surely, 2^21645879 is an apocalyptic number.

21645879 is a deficient number, since it is larger than the sum of its proper divisors (8913081).

21645879 is a wasteful number, since it uses less digits than its factorization.

21645879 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 424449.

The product of its digits is 120960, while the sum is 42.

The square root of 21645879 is about 4652.5131918136. The cubic root of 21645879 is about 278.6923678502.

The spelling of 21645879 in words is "twenty-one million, six hundred forty-five thousand, eight hundred seventy-nine".