638666 has 24 divisors (see below), whose sum is σ = 1176480. Its totient is φ = 259308.

The previous prime is 638663. The next prime is 638669. The reversal of 638666 is 666836.

It is an interprime number because it is at equal distance from previous prime (638663) and next prime (638669).

638666 is a modest number, since divided by 666 gives 638 as remainder.

It is a nialpdrome in base 7.

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 11 ways as a sum of consecutive naturals, for example, 33605 + ... + 33623.

It is an arithmetic number, because the mean of its divisors is an integer number (49020).

2⁶³⁸⁶⁶⁶ is an apocalyptic number.

638666 is a deficient number, since it is larger than the sum of its proper divisors (537814).

638666 is an frugal number, since it uses more digits than its factorization.

638666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 56 (or 28 counting only the distinct ones).

The product of its digits is 31104, while the sum is 35.

The square root of 638666 is about 799.1658150847. The cubic root of 638666 is about 86.1174706214.

The spelling of 638666 in words is "six hundred thirty-eight thousand, six hundred sixty-six".