643637 has 4 divisors (see below), whose sum is σ = 681516. Its totient is φ = 605760.

The previous prime is 643633. The next prime is 643639. The reversal of 643637 is 736346.

643637 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 579121 + 64516 = 761^2 + 254^2 .

It is a cyclic number.

It is not a de Polignac number, because 643637 - 2² = 643633 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643633) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 18914 + ... + 18947.

It is an arithmetic number, because the mean of its divisors is an integer number (170379).

2⁶⁴³⁶³⁷ is an apocalyptic number.

It is an amenable number.

643637 is a deficient number, since it is larger than the sum of its proper divisors (37879).

643637 is a wasteful number, since it uses less digits than its factorization.

643637 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 37878.

The product of its digits is 9072, while the sum is 29.

The square root of 643637 is about 802.2699047079. The cubic root of 643637 is about 86.3403226586.

The spelling of 643637 in words is "six hundred forty-three thousand, six hundred thirty-seven".