638125021 has 2 divisors, whose sum is σ = 638125022. Its totient is φ = 638125020.

The previous prime is 638125009. The next prime is 638125027. The reversal of 638125021 is 120521836.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 617522500 + 20602521 = 24850^2 + 4539^2 .

It is a cyclic number.

It is not a de Polignac number, because 638125021 - 2⁵ = 638124989 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (638125027) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319062510 + 319062511.

It is an arithmetic number, because the mean of its divisors is an integer number (319062511).

Almost surely, 2^638125021 is an apocalyptic number.

It is an amenable number.

638125021 is a deficient number, since it is larger than the sum of its proper divisors (1).

638125021 is an equidigital number, since it uses as much as digits as its factorization.

638125021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2880, while the sum is 28.

The square root of 638125021 is about 25261.1365737965. The cubic root of 638125021 is about 860.9314862142.

Adding to 638125021 its reverse (120521836), we get a palindrome (758646857).

The spelling of 638125021 in words is "six hundred thirty-eight million, one hundred twenty-five thousand, twenty-one".