1643639 has 2 divisors, whose sum is σ = 1643640. Its totient is φ = 1643638.

The previous prime is 1643623. The next prime is 1643641. The reversal of 1643639 is 9363461.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1643639 - 2⁴ = 1643623 is a prime.

Together with 1643641, it forms a pair of twin primes.

It is a Chen prime.

It is an Ulam number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1643659) 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, 821819 + 821820.

It is an arithmetic number, because the mean of its divisors is an integer number (821820).

2^1643639 is an apocalyptic number.

1643639 is a deficient number, since it is larger than the sum of its proper divisors (1).

1643639 is an equidigital number, since it uses as much as digits as its factorization.

1643639 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 11664, while the sum is 32.

The square root of 1643639 is about 1282.0448510095. The cubic root of 1643639 is about 118.0145294759.

The spelling of 1643639 in words is "one million, six hundred forty-three thousand, six hundred thirty-nine".