20979778 has 4 divisors (see below), whose sum is σ = 31469670. Its totient is φ = 10489888.

The previous prime is 20979737. The next prime is 20979779. The reversal of 20979778 is 87797902.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 13010449 + 7969329 = 3607^2 + 2823^2 .

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (20979779) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5244943 + ... + 5244946.

Almost surely, 2^20979778 is an apocalyptic number.

20979778 is a deficient number, since it is larger than the sum of its proper divisors (10489892).

20979778 is a wasteful number, since it uses less digits than its factorization.

20979778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10489891.

The product of its (nonzero) digits is 444528, while the sum is 49.

The square root of 20979778 is about 4580.3687624470. The cubic root of 20979778 is about 275.8038321107.

The spelling of 20979778 in words is "twenty million, nine hundred seventy-nine thousand, seven hundred seventy-eight".