640661979 has 8 divisors (see below), whose sum is σ = 856471360. Its totient is φ = 425980296.

The previous prime is 640661963. The next prime is 640661999. The reversal of 640661979 is 979166046.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 640661979 - 2⁴ = 640661963 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640661929) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 280597 + ... + 282870.

It is an arithmetic number, because the mean of its divisors is an integer number (107058920).

Almost surely, 2^640661979 is an apocalyptic number.

640661979 is a deficient number, since it is larger than the sum of its proper divisors (215809381).

640661979 is a wasteful number, since it uses less digits than its factorization.

640661979 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 563849.

The product of its (nonzero) digits is 489888, while the sum is 48.

The square root of 640661979 is about 25311.3014086593. The cubic root of 640661979 is about 862.0708966546.

The spelling of 640661979 in words is "six hundred forty million, six hundred sixty-one thousand, nine hundred seventy-nine".