638665 has 4 divisors (see below), whose sum is σ = 766404. Its totient is φ = 510928.

The previous prime is 638663. The next prime is 638669. The reversal of 638665 is 566836.

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 80656 + 558009 = 284^2 + 747^2 .

It is a cyclic number.

It is not a de Polignac number, because 638665 - 2¹ = 638663 is a prime.

It is a Duffinian number.

638665 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 638665.

It is not an unprimeable number, because it can be changed into a prime (638663) 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, 63862 + ... + 63871.

It is an arithmetic number, because the mean of its divisors is an integer number (191601).

2⁶³⁸⁶⁶⁵ is an apocalyptic number.

It is an amenable number.

638665 is a deficient number, since it is larger than the sum of its proper divisors (127739).

638665 is a wasteful number, since it uses less digits than its factorization.

638665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 127738.

The product of its digits is 25920, while the sum is 34.

The square root of 638665 is about 799.1651894321. The cubic root of 638665 is about 86.1174256748.

The spelling of 638665 in words is "six hundred thirty-eight thousand, six hundred sixty-five".