640826751 has 4 divisors (see below), whose sum is σ = 854435672. Its totient is φ = 427217832.

The previous prime is 640826723. The next prime is 640826779. The reversal of 640826751 is 157628046.

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

It is an interprime number because it is at equal distance from previous prime (640826723) and next prime (640826779).

It is not a de Polignac number, because 640826751 - 2⁹ = 640826239 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 (640826651) 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, 106804456 + ... + 106804461.

It is an arithmetic number, because the mean of its divisors is an integer number (213608918).

Almost surely, 2^640826751 is an apocalyptic number.

640826751 is a deficient number, since it is larger than the sum of its proper divisors (213608921).

640826751 is a wasteful number, since it uses less digits than its factorization.

640826751 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 213608920.

The product of its (nonzero) digits is 80640, while the sum is 39.

The square root of 640826751 is about 25314.5561090847. The cubic root of 640826751 is about 862.1447957229.

The spelling of 640826751 in words is "six hundred forty million, eight hundred twenty-six thousand, seven hundred fifty-one".