2778649921 has 4 divisors (see below), whose sum is σ = 2831077332. Its totient is φ = 2726222512.

The previous prime is 2778649919. The next prime is 2778649931. The reversal of 2778649921 is 1299468772.

2778649921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It can be written as a sum of positive squares in 2 ways, for example, as 1889119296 + 889530625 = 43464^2 + 29825^2 .

It is a cyclic number.

It is not a de Polignac number, because 2778649921 - 2¹ = 2778649919 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2778649931) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26213626 + ... + 26213731.

It is an arithmetic number, because the mean of its divisors is an integer number (707769333).

Almost surely, 2^2778649921 is an apocalyptic number.

It is an amenable number.

2778649921 is a deficient number, since it is larger than the sum of its proper divisors (52427411).

2778649921 is an equidigital number, since it uses as much as digits as its factorization.

2778649921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 52427410.

The product of its digits is 3048192, while the sum is 55.

The square root of 2778649921 is about 52712.9008972187. The cubic root of 2778649921 is about 1405.8682122584.

The spelling of 2778649921 in words is "two billion, seven hundred seventy-eight million, six hundred forty-nine thousand, nine hundred twenty-one".