643542721 has 2 divisors, whose sum is σ = 643542722. Its totient is φ = 643542720.

The previous prime is 643542709. The next prime is 643542791. The reversal of 643542721 is 127245346.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 478034496 + 165508225 = 21864^2 + 12865^2 .

It is a cyclic number.

It is not a de Polignac number, because 643542721 - 2⁵ = 643542689 is a prime.

It is not a weakly prime, because it can be changed into another prime (643542791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321771360 + 321771361.

It is an arithmetic number, because the mean of its divisors is an integer number (321771361).

Almost surely, 2^643542721 is an apocalyptic number.

It is an amenable number.

643542721 is a deficient number, since it is larger than the sum of its proper divisors (1).

643542721 is an equidigital number, since it uses as much as digits as its factorization.

643542721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 40320, while the sum is 34.

The square root of 643542721 is about 25368.1438225188. The cubic root of 643542721 is about 863.3610678501.

The spelling of 643542721 in words is "six hundred forty-three million, five hundred forty-two thousand, seven hundred twenty-one".