20979881 has 8 divisors (see below), whose sum is σ = 22848840. Its totient is φ = 19147392.

The previous prime is 20979877. The next prime is 20979899. The reversal of 20979881 is 18897902.

It can be written as a sum of positive squares in 4 ways, for example, as 3481 + 20976400 = 59^2 + 4580^2 .

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 20979881 - 2² = 20979877 is a prime.

It is a super-2 number, since 2×20979881² = 880310813548322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20975881) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7910 + ... + 10223.

It is an arithmetic number, because the mean of its divisors is an integer number (2856105).

Almost surely, 2^20979881 is an apocalyptic number.

It is an amenable number.

20979881 is a deficient number, since it is larger than the sum of its proper divisors (1868959).

20979881 is a wasteful number, since it uses less digits than its factorization.

20979881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18235.

The product of its (nonzero) digits is 72576, while the sum is 44.

The square root of 20979881 is about 4580.3800060694. The cubic root of 20979881 is about 275.8042834619.

The spelling of 20979881 in words is "twenty million, nine hundred seventy-nine thousand, eight hundred eighty-one".