640666987 has 6 divisors (see below), whose sum is σ = 662001324. Its totient is φ = 619999380.

The previous prime is 640666969. The next prime is 640666991. The reversal of 640666987 is 789666046.

It is not a de Polignac number, because 640666987 - 2¹⁵ = 640634219 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640666387) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 332373 + ... + 334294.

It is an arithmetic number, because the mean of its divisors is an integer number (110333554).

Almost surely, 2^640666987 is an apocalyptic number.

640666987 is a deficient number, since it is larger than the sum of its proper divisors (21334337).

640666987 is an equidigital number, since it uses as much as digits as its factorization.

640666987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 666729 (or 666698 counting only the distinct ones).

The product of its (nonzero) digits is 2612736, while the sum is 52.

The square root of 640666987 is about 25311.4003366072. The cubic root of 640666987 is about 862.0731428937.

The spelling of 640666987 in words is "six hundred forty million, six hundred sixty-six thousand, nine hundred eighty-seven".