640634 has 4 divisors (see below), whose sum is σ = 960954. Its totient is φ = 320316.

The previous prime is 640631. The next prime is 640649. The reversal of 640634 is 436046.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 483025 + 157609 = 695^2 + 397^2 .

It is not an unprimeable number, because it can be changed into a prime (640631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 160157 + ... + 160160.

2⁶⁴⁰⁶³⁴ is an apocalyptic number.

640634 is a deficient number, since it is larger than the sum of its proper divisors (320320).

640634 is a wasteful number, since it uses less digits than its factorization.

640634 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 320319.

The product of its (nonzero) digits is 1728, while the sum is 23.

The square root of 640634 is about 800.3961519148. The cubic root of 640634 is about 86.2058347014.

The spelling of 640634 in words is "six hundred forty thousand, six hundred thirty-four".