640811761 has 4 divisors (see below), whose sum is σ = 640872000. Its totient is φ = 640751524.

The previous prime is 640811747. The next prime is 640811807. The reversal of 640811761 is 167118046.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 640811761 - 2⁵ = 640811729 is a prime.

It is a super-2 number, since 2×640811761² = 821279426071842242, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640811741) 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, 9421 + ... + 37018.

It is an arithmetic number, because the mean of its divisors is an integer number (160218000).

Almost surely, 2^640811761 is an apocalyptic number.

It is an amenable number.

640811761 is a deficient number, since it is larger than the sum of its proper divisors (60239).

640811761 is a wasteful number, since it uses less digits than its factorization.

640811761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 60238.

The product of its (nonzero) digits is 8064, while the sum is 34.

The square root of 640811761 is about 25314.2600326377. The cubic root of 640811761 is about 862.1380733385.

The spelling of 640811761 in words is "six hundred forty million, eight hundred eleven thousand, seven hundred sixty-one".