639199781 has 4 divisors (see below), whose sum is σ = 697308864. Its totient is φ = 581090700.

The previous prime is 639199777. The next prime is 639199801. The reversal of 639199781 is 187991936.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 639199781 - 2² = 639199777 is a prime.

It is a super-2 number, since 2×639199781² = 817152720060895922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639199181) 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 in 3 ways as a sum of consecutive naturals, for example, 29054525 + ... + 29054546.

It is an arithmetic number, because the mean of its divisors is an integer number (174327216).

Almost surely, 2^639199781 is an apocalyptic number.

It is an amenable number.

639199781 is a deficient number, since it is larger than the sum of its proper divisors (58109083).

639199781 is a wasteful number, since it uses less digits than its factorization.

639199781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 58109082.

The product of its digits is 734832, while the sum is 53.

The square root of 639199781 is about 25282.4006178211. The cubic root of 639199781 is about 861.4145554688.

The spelling of 639199781 in words is "six hundred thirty-nine million, one hundred ninety-nine thousand, seven hundred eighty-one".