638949021 has 4 divisors (see below), whose sum is σ = 851932032. Its totient is φ = 425966012.

The previous prime is 638949013. The next prime is 638949049. The reversal of 638949021 is 120949836.

638949021 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 638949021 - 2³ = 638949013 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (638949221) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 106491501 + ... + 106491506.

It is an arithmetic number, because the mean of its divisors is an integer number (212983008).

Almost surely, 2^638949021 is an apocalyptic number.

It is an amenable number.

638949021 is a deficient number, since it is larger than the sum of its proper divisors (212983011).

638949021 is a wasteful number, since it uses less digits than its factorization.

638949021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 212983010.

The product of its (nonzero) digits is 93312, while the sum is 42.

The square root of 638949021 is about 25277.4409503810. The cubic root of 638949021 is about 861.3018955601.

The spelling of 638949021 in words is "six hundred thirty-eight million, nine hundred forty-nine thousand, twenty-one".