640978829 has 4 divisors (see below), whose sum is σ = 678683484. Its totient is φ = 603274176.

The previous prime is 640978781. The next prime is 640978837. The reversal of 640978829 is 928879046.

640978829 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, and also an emirpimes, since its reverse is a distinct semiprime: 928879046 = 2 ⋅464439523.

It can be written as a sum of positive squares in 2 ways, for example, as 519384100 + 121594729 = 22790^2 + 11027^2 .

It is a cyclic number.

It is not a de Polignac number, because 640978829 - 2²⁰ = 639930253 is a prime.

It is a super-2 number, since 2×640978829² = 821707718452422482, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640978859) 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, 18852302 + ... + 18852335.

It is an arithmetic number, because the mean of its divisors is an integer number (169670871).

Almost surely, 2^640978829 is an apocalyptic number.

It is an amenable number.

640978829 is a deficient number, since it is larger than the sum of its proper divisors (37704655).

640978829 is a wasteful number, since it uses less digits than its factorization.

640978829 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37704654.

The product of its (nonzero) digits is 1741824, while the sum is 53.

The square root of 640978829 is about 25317.5596967796. The cubic root of 640978829 is about 862.2129903822.

The spelling of 640978829 in words is "six hundred forty million, nine hundred seventy-eight thousand, eight hundred twenty-nine".