638721 has 6 divisors (see below), whose sum is σ = 922610. Its totient is φ = 425808.

The previous prime is 638719. The next prime is 638767. The reversal of 638721 is 127836.

638721 is a `hidden beast` number, since 638 + 7 + 21 = 666.

638721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 408321 + 230400 = 639^2 + 480^2 .

It is not a de Polignac number, because 638721 - 2¹ = 638719 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a plaindrome in base 14.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 638721.

It is not an unprimeable number, because it can be changed into a prime (638621) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 35476 + ... + 35493.

2⁶³⁸⁷²¹ is an apocalyptic number.

It is an amenable number.

638721 is a deficient number, since it is larger than the sum of its proper divisors (283889).

638721 is a wasteful number, since it uses less digits than its factorization.

638721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 70975 (or 70972 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 638721 is about 799.2002252252. The cubic root of 638721 is about 86.1199426098.

The spelling of 638721 in words is "six hundred thirty-eight thousand, seven hundred twenty-one".