639216781 has 16 divisors (see below), whose sum is σ = 745242624. Its totient is φ = 536974704.

The previous prime is 639216757. The next prime is 639216827. The reversal of 639216781 is 187612936.

It is not a de Polignac number, because 639216781 - 2⁵ = 639216749 is a prime.

It is a super-2 number, since 2×639216781² = 817196186224003922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639216731) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 69456 + ... + 78118.

It is an arithmetic number, because the mean of its divisors is an integer number (46577664).

Almost surely, 2^639216781 is an apocalyptic number.

It is an amenable number.

639216781 is a deficient number, since it is larger than the sum of its proper divisors (106025843).

639216781 is a wasteful number, since it uses less digits than its factorization.

639216781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8880.

The product of its digits is 108864, while the sum is 43.

The square root of 639216781 is about 25282.7368178368. The cubic root of 639216781 is about 861.4221920576.

The spelling of 639216781 in words is "six hundred thirty-nine million, two hundred sixteen thousand, seven hundred eighty-one".