640661505 has 32 divisors (see below), whose sum is σ = 1133585280. Its totient is φ = 306362880.

The previous prime is 640661501. The next prime is 640661519. The reversal of 640661505 is 505166046.

It is not a de Polignac number, because 640661505 - 2² = 640661501 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is not an unprimeable number, because it can be changed into a prime (640661501) by changing a digit.

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 31 ways as a sum of consecutive naturals, for example, 14550 + ... + 38639.

It is an arithmetic number, because the mean of its divisors is an integer number (35424540).

Almost surely, 2^640661505 is an apocalyptic number.

It is an amenable number.

640661505 is a deficient number, since it is larger than the sum of its proper divisors (492923775).

640661505 is a wasteful number, since it uses less digits than its factorization.

640661505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53281.

The product of its (nonzero) digits is 21600, while the sum is 33.

The square root of 640661505 is about 25311.2920452513. The cubic root of 640661505 is about 862.0706840507.

The spelling of 640661505 in words is "six hundred forty million, six hundred sixty-one thousand, five hundred five".