640494865 has 16 divisors (see below), whose sum is σ = 777720528. Its totient is φ = 506346496.

The previous prime is 640494817. The next prime is 640494913. The reversal of 640494865 is 568494046.

It is a Cunningham number, because it is equal to 25308²+1.

It is an interprime number because it is at equal distance from previous prime (640494817) and next prime (640494913).

It can be written as a sum of positive squares in 8 ways, for example, as 1 + 640494864 = 1^2 + 25308^2 .

It is a cyclic number.

It is not a de Polignac number, because 640494865 - 2¹¹ = 640492817 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 157599 + ... + 161611.

It is an arithmetic number, because the mean of its divisors is an integer number (48607533).

Almost surely, 2^640494865 is an apocalyptic number.

It is an amenable number.

640494865 is a deficient number, since it is larger than the sum of its proper divisors (137225663).

640494865 is a wasteful number, since it uses less digits than its factorization.

640494865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4388.

The product of its (nonzero) digits is 829440, while the sum is 46.

The square root of 640494865 is about 25308.0000197566. Note that the first 4 decimals coincide. The cubic root of 640494865 is about 861.9959342727.

The spelling of 640494865 in words is "six hundred forty million, four hundred ninety-four thousand, eight hundred sixty-five".