638961971 has 4 divisors (see below), whose sum is σ = 646660392. Its totient is φ = 631263552.

The previous prime is 638961941. The next prime is 638961979. The reversal of 638961971 is 179169836.

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

It is a cyclic number.

It is not a de Polignac number, because 638961971 - 2⁶ = 638961907 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (638961979) 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, 3849086 + ... + 3849251.

It is an arithmetic number, because the mean of its divisors is an integer number (161665098).

Almost surely, 2^638961971 is an apocalyptic number.

638961971 is a deficient number, since it is larger than the sum of its proper divisors (7698421).

638961971 is an equidigital number, since it uses as much as digits as its factorization.

638961971 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7698420.

The product of its digits is 489888, while the sum is 50.

The square root of 638961971 is about 25277.6971063426. The cubic root of 638961971 is about 861.3077143781.

The spelling of 638961971 in words is "six hundred thirty-eight million, nine hundred sixty-one thousand, nine hundred seventy-one".