640669 has 2 divisors, whose sum is σ = 640670. Its totient is φ = 640668.

The previous prime is 640667. The next prime is 640687. The reversal of 640669 is 966046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 580644 + 60025 = 762^2 + 245^2 .

It is a cyclic number.

It is not a de Polignac number, because 640669 - 2¹ = 640667 is a prime.

It is a super-2 number, since 2×640669² = 820913535122, which contains 22 as substring.

Together with 640667, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 640669.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640663) 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, 320334 + 320335.

It is an arithmetic number, because the mean of its divisors is an integer number (320335).

2⁶⁴⁰⁶⁶⁹ is an apocalyptic number.

It is an amenable number.

640669 is a deficient number, since it is larger than the sum of its proper divisors (1).

640669 is an equidigital number, since it uses as much as digits as its factorization.

640669 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 7776, while the sum is 31.

The square root of 640669 is about 800.4180157892. The cubic root of 640669 is about 86.2074045782.

The spelling of 640669 in words is "six hundred forty thousand, six hundred sixty-nine".