638709121 has 2 divisors, whose sum is σ = 638709122. Its totient is φ = 638709120.

The previous prime is 638709119. The next prime is 638709131. The reversal of 638709121 is 121907836.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 631818496 + 6890625 = 25136^2 + 2625^2 .

It is a cyclic number.

It is not a de Polignac number, because 638709121 - 2¹ = 638709119 is a prime.

Together with 638709119, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (638709131) 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, 319354560 + 319354561.

It is an arithmetic number, because the mean of its divisors is an integer number (319354561).

Almost surely, 2^638709121 is an apocalyptic number.

It is an amenable number.

638709121 is a deficient number, since it is larger than the sum of its proper divisors (1).

638709121 is an equidigital number, since it uses as much as digits as its factorization.

638709121 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 18144, while the sum is 37.

The square root of 638709121 is about 25272.6951669188. The cubic root of 638709121 is about 861.1940871730.

The spelling of 638709121 in words is "six hundred thirty-eight million, seven hundred nine thousand, one hundred twenty-one".