640667 has 2 divisors, whose sum is σ = 640668. Its totient is φ = 640666.

The previous prime is 640663. The next prime is 640669. The reversal of 640667 is 766046.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 640667 - 2² = 640663 is a prime.

Together with 640669, it forms a pair of twin primes.

It is a Chen prime.

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, 320333 + 320334.

It is an arithmetic number, because the mean of its divisors is an integer number (320334).

2⁶⁴⁰⁶⁶⁷ is an apocalyptic number.

640667 is a deficient number, since it is larger than the sum of its proper divisors (1).

640667 is an equidigital number, since it uses as much as digits as its factorization.

640667 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6048, while the sum is 29.

The square root of 640667 is about 800.4167664411. The cubic root of 640667 is about 86.2073148725.

The spelling of 640667 in words is "six hundred forty thousand, six hundred sixty-seven".