643421 has 2 divisors, whose sum is σ = 643422. Its totient is φ = 643420.

The previous prime is 643403. The next prime is 643429. The reversal of 643421 is 124346.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 624100 + 19321 = 790^2 + 139^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643421 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 643393 and 643402.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (643429) by changing a digit.

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

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321710 + 321711.

It is an arithmetic number, because the mean of its divisors is an integer number (321711).

2⁶⁴³⁴²¹ is an apocalyptic number.

It is an amenable number.

643421 is a deficient number, since it is larger than the sum of its proper divisors (1).

643421 is an equidigital number, since it uses as much as digits as its factorization.

643421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 576, while the sum is 20.

The square root of 643421 is about 802.1352753744. The cubic root of 643421 is about 86.3306631786.

Adding to 643421 its reverse (124346), we get a palindrome (767767).

The spelling of 643421 in words is "six hundred forty-three thousand, four hundred twenty-one".