638428891 has 2 divisors, whose sum is σ = 638428892. Its totient is φ = 638428890.

The previous prime is 638428883. The next prime is 638428919. The reversal of 638428891 is 198824836.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 638428891 - 2³ = 638428883 is a prime.

It is not a weakly prime, because it can be changed into another prime (638428391) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 319214445 + 319214446.

It is an arithmetic number, because the mean of its divisors is an integer number (319214446).

Almost surely, 2^638428891 is an apocalyptic number.

638428891 is a deficient number, since it is larger than the sum of its proper divisors (1).

638428891 is an equidigital number, since it uses as much as digits as its factorization.

638428891 is an evil number, because the sum of its binary digits is even.

The product of its digits is 663552, while the sum is 49.

The square root of 638428891 is about 25267.1504329238. The cubic root of 638428891 is about 861.0681207437.

The spelling of 638428891 in words is "six hundred thirty-eight million, four hundred twenty-eight thousand, eight hundred ninety-one".