21208979 has 8 divisors (see below), whose sum is σ = 24498288. Its totient is φ = 18146560.

The previous prime is 21208969. The next prime is 21208981. The reversal of 21208979 is 97980212.

21208979 = T₁₃₂ + T₁₃₃ + ... + T₅₀₅.

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

It is a cyclic number.

It is not a de Polignac number, because 21208979 - 2²⁰ = 20160403 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21208919) 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, 56522 + ... + 56895.

It is an arithmetic number, because the mean of its divisors is an integer number (3062286).

Almost surely, 2^21208979 is an apocalyptic number.

21208979 is a deficient number, since it is larger than the sum of its proper divisors (3289309).

21208979 is a wasteful number, since it uses less digits than its factorization.

21208979 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 113445.

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

The square root of 21208979 is about 4605.3207271590. The cubic root of 21208979 is about 276.8045687583.

The spelling of 21208979 in words is "twenty-one million, two hundred eight thousand, nine hundred seventy-nine".