9921813778 has 16 divisors (see below), whose sum is σ = 15250268376. Its totient is φ = 4838463360.

The previous prime is 9921813731. The next prime is 9921813809. The reversal of 9921813778 is 8773181299.

9921813778 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 4 ways, for example, as 8358164929 + 1563648849 = 91423^2 + 39543^2 .

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 289900 + ... + 322312.

Almost surely, 2^9921813778 is an apocalyptic number.

9921813778 is a deficient number, since it is larger than the sum of its proper divisors (5328454598).

9921813778 is a wasteful number, since it uses less digits than its factorization.

9921813778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36189.

The product of its digits is 1524096, while the sum is 55.

The square root of 9921813778 is about 99608.3017524142. The cubic root of 9921813778 is about 2148.8050888996.

The spelling of 9921813778 in words is "nine billion, nine hundred twenty-one million, eight hundred thirteen thousand, seven hundred seventy-eight".