643639 has 2 divisors, whose sum is σ = 643640. Its totient is φ = 643638.

The previous prime is 643633. The next prime is 643649. The reversal of 643639 is 936346.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643639 is a prime.

It is a nialpdrome in base 15.

It is a self number, because there is not a number n which added to its sum of digits gives 643639.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (643633) 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, 321819 + 321820.

It is an arithmetic number, because the mean of its divisors is an integer number (321820).

2⁶⁴³⁶³⁹ is an apocalyptic number.

643639 is a deficient number, since it is larger than the sum of its proper divisors (1).

643639 is an equidigital number, since it uses as much as digits as its factorization.

643639 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 11664, while the sum is 31.

The square root of 643639 is about 802.2711511702. The cubic root of 643639 is about 86.3404120882.

The spelling of 643639 in words is "six hundred forty-three thousand, six hundred thirty-nine".