638782021 has 4 divisors (see below), whose sum is σ = 676357452. Its totient is φ = 601206592.

The previous prime is 638781937. The next prime is 638782031. The reversal of 638782021 is 120287836.

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 266832225 + 371949796 = 16335^2 + 19286^2 .

It is a cyclic number.

It is not a de Polignac number, because 638782021 - 2⁹ = 638781509 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (638782031) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 18787690 + ... + 18787723.

It is an arithmetic number, because the mean of its divisors is an integer number (169089363).

Almost surely, 2^638782021 is an apocalyptic number.

It is an amenable number.

638782021 is a deficient number, since it is larger than the sum of its proper divisors (37575431).

638782021 is a wasteful number, since it uses less digits than its factorization.

638782021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37575430.

The product of its (nonzero) digits is 32256, while the sum is 37.

The square root of 638782021 is about 25274.1373937866. The cubic root of 638782021 is about 861.2268504756.

The spelling of 638782021 in words is "six hundred thirty-eight million, seven hundred eighty-two thousand, twenty-one".