643 has 2 divisors, whose sum is σ = 644. Its totient is φ = 642.

The previous prime is 641. The next prime is 647. The reversal of 643 is 346.

643 is nontrivially palindromic in base 11.

It is a weak prime.

643 is a truncatable prime.

It is a cyclic number.

It is not a de Polignac number, because 643 - 2^{1} = 641 is a prime.

Together with 641, it forms a pair of twin primes.

643 is an undulating number in base 11.

643 is a lucky number.

It is a plaindrome in base 12, base 14 and base 15.

It is a nialpdrome in base 10.

It is not a weakly prime, because it can be changed into another prime (641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321 + 322.

It is an arithmetic number, because the mean of its divisors is an integer number (322).

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

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

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

The product of its digits is 72, while the sum is 13.

The square root of 643 is about 25.3574446662. The cubic root of 643 is about 8.6311829922.

Adding to 643 its sum of digits (13), we get a palindrome (656).

Subtracting from 643 its sum of digits (13), we obtain a triangular number (630 = T_{35}).

Adding to 643 its reverse (346), we get a palindrome (989).

It can be divided in two parts, 6 and 43, that added together give a square (49 = 7^{2}).

The spelling of 643 in words is "six hundred forty-three", and thus it is an aban number.

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