643631 has 4 divisors (see below), whose sum is σ = 654600. Its totient is φ = 632664.

The previous prime is 643619. The next prime is 643633. The reversal of 643631 is 136346.

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

It is a cyclic number.

It is not a de Polignac number, because 643631 - 2⁶ = 643567 is a prime.

It is a super-2 number, since 2×643631² = 828521728322, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 643597 and 643606.

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 pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5396 + ... + 5513.

It is an arithmetic number, because the mean of its divisors is an integer number (163650).

2⁶⁴³⁶³¹ is an apocalyptic number.

643631 is a deficient number, since it is larger than the sum of its proper divisors (10969).

643631 is a wasteful number, since it uses less digits than its factorization.

643631 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10968.

The product of its digits is 1296, while the sum is 23.

The square root of 643631 is about 802.2661653092. The cubic root of 643631 is about 86.3400543689.

Adding to 643631 its reverse (136346), we get a palindrome (779977).

The spelling of 643631 in words is "six hundred forty-three thousand, six hundred thirty-one".