638921 has 4 divisors (see below), whose sum is σ = 640644. Its totient is φ = 637200.

The previous prime is 638893. The next prime is 638923. The reversal of 638921 is 129836.

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 440896 + 198025 = 664^2 + 445^2 .

It is a cyclic number.

It is not a de Polignac number, because 638921 - 2⁶ = 638857 is a prime.

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

It is a Duffinian number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 638921.

It is not an unprimeable number, because it can be changed into a prime (638923) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 50 + ... + 1131.

It is an arithmetic number, because the mean of its divisors is an integer number (160161).

2⁶³⁸⁹²¹ is an apocalyptic number.

It is an amenable number.

638921 is a deficient number, since it is larger than the sum of its proper divisors (1723).

638921 is a wasteful number, since it uses less digits than its factorization.

638921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1722.

The product of its digits is 2592, while the sum is 29.

The square root of 638921 is about 799.3253405216. The cubic root of 638921 is about 86.1289304627.

The spelling of 638921 in words is "six hundred thirty-eight thousand, nine hundred twenty-one".