643905 has 24 divisors (see below), whose sum is σ = 1146600. Its totient is φ = 334080.

The previous prime is 643889. The next prime is 643919. The reversal of 643905 is 509346.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 16641 + 627264 = 129^2 + 792^2 .

It is not a de Polignac number, because 643905 - 2⁴ = 643889 is a prime.

It is a super-2 number, since 2×643905² = 829227298050, which contains 22 as substring.

643905 is a lucky number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1671 + ... + 2019.

It is an arithmetic number, because the mean of its divisors is an integer number (47775).

2⁶⁴³⁹⁰⁵ is an apocalyptic number.

It is an amenable number.

643905 is a deficient number, since it is larger than the sum of its proper divisors (502695).

643905 is a wasteful number, since it uses less digits than its factorization.

643905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 401 (or 398 counting only the distinct ones).

The product of its (nonzero) digits is 3240, while the sum is 27.

The square root of 643905 is about 802.4369134082. The cubic root of 643905 is about 86.3523045654.

It can be divided in two parts, 64 and 3905, that added together give a square (3969 = 63²).

The spelling of 643905 in words is "six hundred forty-three thousand, nine hundred five".