639540 has 144 divisors (see below), whose sum is σ = 2358720. Its totient is φ = 138240.

The previous prime is 639533. The next prime is 639547. The reversal of 639540 is 45936.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (639533) and next prime (639547).

It is a super-2 number, since 2×639540² = 818022823200, which contains 22 as substring.

It is a nialpdrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639547) by changing a digit.

639540 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 47 ways as a sum of consecutive naturals, for example, 33651 + ... + 33669.

It is an arithmetic number, because the mean of its divisors is an integer number (16380).

2⁶³⁹⁵⁴⁰ is an apocalyptic number.

639540 is a gapful number since it is divisible by the number (60) 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 639540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1179360).

639540 is an abundant number, since it is smaller than the sum of its proper divisors (1719180).

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

639540 is a wasteful number, since it uses less digits than its factorization.

639540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 62 (or 57 counting only the distinct ones).

The product of its (nonzero) digits is 3240, while the sum is 27.

The square root of 639540 is about 799.7124483213. The cubic root of 639540 is about 86.1567359869.

The spelling of 639540 in words is "six hundred thirty-nine thousand, five hundred forty".