638779 has 4 divisors (see below), whose sum is σ = 666576. Its totient is φ = 610984.

The previous prime is 638767. The next prime is 638801. The reversal of 638779 is 977836.

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

It is a cyclic number.

It is not a de Polignac number, because 638779 - 2¹¹ = 636731 is a prime.

It is a super-2 number, since 2×638779² = 816077221682, which contains 22 as substring.

It is a Duffinian number.

638779 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (638719) 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, 13864 + ... + 13909.

It is an arithmetic number, because the mean of its divisors is an integer number (166644).

2⁶³⁸⁷⁷⁹ is an apocalyptic number.

638779 is a deficient number, since it is larger than the sum of its proper divisors (27797).

638779 is a wasteful number, since it uses less digits than its factorization.

638779 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27796.

The product of its digits is 63504, while the sum is 40.

The square root of 638779 is about 799.2365106775. The cubic root of 638779 is about 86.1225492803.

The spelling of 638779 in words is "six hundred thirty-eight thousand, seven hundred seventy-nine".