639190091 has 4 divisors (see below), whose sum is σ = 639981000. Its totient is φ = 638399184.

The previous prime is 639190043. The next prime is 639190093. The reversal of 639190091 is 190091936.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-639190091 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (639190093) 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, 394241 + ... + 395858.

It is an arithmetic number, because the mean of its divisors is an integer number (159995250).

Almost surely, 2^639190091 is an apocalyptic number.

639190091 is a deficient number, since it is larger than the sum of its proper divisors (790909).

639190091 is an equidigital number, since it uses as much as digits as its factorization.

639190091 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 790908.

The product of its (nonzero) digits is 13122, while the sum is 38.

The square root of 639190091 is about 25282.2089818117. The cubic root of 639190091 is about 861.4102025526.

The spelling of 639190091 in words is "six hundred thirty-nine million, one hundred ninety thousand, ninety-one".