643857421 has 2 divisors, whose sum is σ = 643857422. Its totient is φ = 643857420.

The previous prime is 643857373. The next prime is 643857433. The reversal of 643857421 is 124758346.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 500193225 + 143664196 = 22365^2 + 11986^2 .

It is a cyclic number.

It is not a de Polignac number, because 643857421 - 2⁷ = 643857293 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (643857121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321928710 + 321928711.

It is an arithmetic number, because the mean of its divisors is an integer number (321928711).

Almost surely, 2^643857421 is an apocalyptic number.

It is an amenable number.

643857421 is a deficient number, since it is larger than the sum of its proper divisors (1).

643857421 is an equidigital number, since it uses as much as digits as its factorization.

643857421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 161280, while the sum is 40.

The square root of 643857421 is about 25374.3457255552. The cubic root of 643857421 is about 863.5017761735.

The spelling of 643857421 in words is "six hundred forty-three million, eight hundred fifty-seven thousand, four hundred twenty-one".