640718609 has 4 divisors (see below), whose sum is σ = 643399680. Its totient is φ = 638037540.

The previous prime is 640718597. The next prime is 640718621. The reversal of 640718609 is 906817046.

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 an emirpimes, since its reverse is a distinct semiprime: 906817046 = 2 ⋅453408523.

It is an interprime number because it is at equal distance from previous prime (640718597) and next prime (640718621).

It is a cyclic number.

It is not a de Polignac number, because 640718609 - 2¹⁶ = 640653073 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640718669) 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, 1340177 + ... + 1340654.

It is an arithmetic number, because the mean of its divisors is an integer number (160849920).

Almost surely, 2^640718609 is an apocalyptic number.

It is an amenable number.

640718609 is a deficient number, since it is larger than the sum of its proper divisors (2681071).

640718609 is a wasteful number, since it uses less digits than its factorization.

640718609 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2681070.

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

The square root of 640718609 is about 25312.4200541947. The cubic root of 640718609 is about 862.0962962351.

The spelling of 640718609 in words is "six hundred forty million, seven hundred eighteen thousand, six hundred nine".