640009 has 2 divisors, whose sum is σ = 640010. Its totient is φ = 640008.

The previous prime is 640007. The next prime is 640019. The reversal of 640009 is 900046.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 640000 + 9 = 800^2 + 3^2 .

It is a cyclic number.

It is not a de Polignac number, because 640009 - 2¹ = 640007 is a prime.

It is a super-2 number, since 2×640009² = 819223040162, which contains 22 as substring.

Together with 640007, it forms a pair of twin primes.

It is a Chen prime.

640009 is a lucky number.

It is a nialpdrome in base 15.

It is not a weakly prime, because it can be changed into another prime (640007) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320004 + 320005.

It is an arithmetic number, because the mean of its divisors is an integer number (320005).

2⁶⁴⁰⁰⁰⁹ is an apocalyptic number.

It is an amenable number.

640009 is a deficient number, since it is larger than the sum of its proper divisors (1).

640009 is an equidigital number, since it uses as much as digits as its factorization.

640009 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 216, while the sum is 19.

The square root of 640009 is about 800.0056249802. The cubic root of 640009 is about 86.1777915559.

It can be divided in two parts, 64000 and 9, that added together give a square (64009 = 253²).

The spelling of 640009 in words is "six hundred forty thousand, nine".