639621 has 6 divisors (see below), whose sum is σ = 923910. Its totient is φ = 426408.

The previous prime is 639601. The next prime is 639631. The reversal of 639621 is 126936.

It is a happy number.

639621 is a `hidden beast` number, since 6 + 39 + 621 = 666.

It can be written as a sum of positive squares in only one way, i.e., 324900 + 314721 = 570^2 + 561^2 .

It is not a de Polignac number, because 639621 - 2⁵ = 639589 is a prime.

It is an Ulam number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639601) 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, 35526 + ... + 35543.

It is an arithmetic number, because the mean of its divisors is an integer number (153985).

2⁶³⁹⁶²¹ is an apocalyptic number.

It is an amenable number.

639621 is a deficient number, since it is larger than the sum of its proper divisors (284289).

639621 is a wasteful number, since it uses less digits than its factorization.

639621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 71075 (or 71072 counting only the distinct ones).

The product of its digits is 1944, while the sum is 27.

The square root of 639621 is about 799.7630899210. The cubic root of 639621 is about 86.1603731850.

The spelling of 639621 in words is "six hundred thirty-nine thousand, six hundred twenty-one".