638928 has 100 divisors (see below), whose sum is σ = 2025540. Its totient is φ = 193536.

The previous prime is 638923. The next prime is 638933. The reversal of 638928 is 829836.

It is an interprime number because it is at equal distance from previous prime (638923) and next prime (638933).

It can be written as a sum of positive squares in 2 ways, for example, as 419904 + 219024 = 648^2 + 468^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 638892 and 638901.

It is a congruent number.

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

638928 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 22018 + ... + 22046.

2⁶³⁸⁹²⁸ is an apocalyptic number.

638928 is a gapful number since it is divisible by the number (68) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 638928, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1012770).

638928 is an abundant number, since it is smaller than the sum of its proper divisors (1386612).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

638928 is a wasteful number, since it uses less digits than its factorization.

638928 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66 (or 51 counting only the distinct ones).

The product of its digits is 20736, while the sum is 36.

The square root of 638928 is about 799.3297192023. The cubic root of 638928 is about 86.1292450036.

The spelling of 638928 in words is "six hundred thirty-eight thousand, nine hundred twenty-eight".