638979 has 24 divisors (see below), whose sum is σ = 1002048. Its totient is φ = 359040.

The previous prime is 638977. The next prime is 638993. The reversal of 638979 is 979836.

It is a happy number.

It is not a de Polignac number, because 638979 - 2¹ = 638977 is a prime.

638979 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 638979.

It is not an unprimeable number, because it can be changed into a prime (638971) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 9504 + ... + 9570.

It is an arithmetic number, because the mean of its divisors is an integer number (41752).

2⁶³⁸⁹⁷⁹ is an apocalyptic number.

638979 is a deficient number, since it is larger than the sum of its proper divisors (363069).

638979 is a wasteful number, since it uses less digits than its factorization.

638979 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 115 (or 98 counting only the distinct ones).

The product of its digits is 81648, while the sum is 42.

The square root of 638979 is about 799.3616202946. The cubic root of 638979 is about 86.1315365892.

The spelling of 638979 in words is "six hundred thirty-eight thousand, nine hundred seventy-nine".