643645 has 8 divisors (see below), whose sum is σ = 780120. Its totient is φ = 509760.

The previous prime is 643639. The next prime is 643649. The reversal of 643645 is 546346.

It can be written as a sum of positive squares in 4 ways, for example, as 248004 + 395641 = 498^2 + 629^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 643645 - 2¹⁵ = 610877 is a prime.

643645 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643649) 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 in 7 ways as a sum of consecutive naturals, for example, 46 + ... + 1135.

It is an arithmetic number, because the mean of its divisors is an integer number (97515).

2⁶⁴³⁶⁴⁵ is an apocalyptic number.

It is an amenable number.

643645 is a deficient number, since it is larger than the sum of its proper divisors (136475).

643645 is a wasteful number, since it uses less digits than its factorization.

643645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1295.

The product of its digits is 8640, while the sum is 28.

The square root of 643645 is about 802.2748905456. The cubic root of 643645 is about 86.3406803757.

The spelling of 643645 in words is "six hundred forty-three thousand, six hundred forty-five".