640068791 has 4 divisors (see below), whose sum is σ = 650561784. Its totient is φ = 629575800.

The previous prime is 640068787. The next prime is 640068829. The reversal of 640068791 is 197860046.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 197860046 = 2 ⋅98930023.

It is a cyclic number.

It is not a de Polignac number, because 640068791 - 2² = 640068787 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640068721) 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, 5246405 + ... + 5246526.

It is an arithmetic number, because the mean of its divisors is an integer number (162640446).

Almost surely, 2^640068791 is an apocalyptic number.

640068791 is a gapful number since it is divisible by the number (61) formed by its first and last digit.

640068791 is a deficient number, since it is larger than the sum of its proper divisors (10492993).

640068791 is a wasteful number, since it uses less digits than its factorization.

640068791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10492992.

The product of its (nonzero) digits is 72576, while the sum is 41.

The square root of 640068791 is about 25299.5808463302. The cubic root of 640068791 is about 861.8047510976.

The spelling of 640068791 in words is "six hundred forty million, sixty-eight thousand, seven hundred ninety-one".