640447 has 4 divisors (see below), whose sum is σ = 643896. Its totient is φ = 637000.

The previous prime is 640421. The next prime is 640457. The reversal of 640447 is 744046.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 744046 = 2 ⋅372023.

It is a cyclic number.

It is not a de Polignac number, because 640447 - 2¹⁹ = 116159 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640457) 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 3 ways as a sum of consecutive naturals, for example, 1429 + ... + 1822.

It is an arithmetic number, because the mean of its divisors is an integer number (160974).

2⁶⁴⁰⁴⁴⁷ is an apocalyptic number.

640447 is a deficient number, since it is larger than the sum of its proper divisors (3449).

640447 is a wasteful number, since it uses less digits than its factorization.

640447 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3448.

The product of its (nonzero) digits is 2688, while the sum is 25.

The square root of 640447 is about 800.2793262355. The cubic root of 640447 is about 86.1974461052.

The spelling of 640447 in words is "six hundred forty thousand, four hundred forty-seven".