21209879 has 6 divisors (see below), whose sum is σ = 21716496. Its totient is φ = 20714820.

The previous prime is 21209873. The next prime is 21209927. The reversal of 21209879 is 97890212.

It is not a de Polignac number, because 21209879 - 2⁸ = 21209623 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21209873) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 3887 + ... + 7584.

It is an arithmetic number, because the mean of its divisors is an integer number (3619416).

Almost surely, 2^21209879 is an apocalyptic number.

21209879 is a deficient number, since it is larger than the sum of its proper divisors (506617).

21209879 is an equidigital number, since it uses as much as digits as its factorization.

21209879 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11557 (or 11514 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 38.

The square root of 21209879 is about 4605.4184391866. The cubic root of 21209879 is about 276.8084840904.

The spelling of 21209879 in words is "twenty-one million, two hundred nine thousand, eight hundred seventy-nine".