640221 has 4 divisors (see below), whose sum is σ = 853632. Its totient is φ = 426812.

The previous prime is 640219. The next prime is 640223. The reversal of 640221 is 122046.

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.

It is an interprime number because it is at equal distance from previous prime (640219) and next prime (640223).

It is a cyclic number.

It is not a de Polignac number, because 640221 - 2¹ = 640219 is a prime.

It is a D-number.

It is a self number, because there is not a number n which added to its sum of digits gives 640221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640223) 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 in 3 ways as a sum of consecutive naturals, for example, 106701 + ... + 106706.

It is an arithmetic number, because the mean of its divisors is an integer number (213408).

2⁶⁴⁰²²¹ is an apocalyptic number.

It is an amenable number.

640221 is a deficient number, since it is larger than the sum of its proper divisors (213411).

640221 is a wasteful number, since it uses less digits than its factorization.

640221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 213410.

The product of its (nonzero) digits is 96, while the sum is 15.

The square root of 640221 is about 800.1381130780. The cubic root of 640221 is about 86.1873058361.

Adding to 640221 its reverse (122046), we get a palindrome (762267).

It can be divided in two parts, 640 and 221, that added together give a triangular number (861 = T₄₁).

The spelling of 640221 in words is "six hundred forty thousand, two hundred twenty-one".