643523921 has 2 divisors, whose sum is σ = 643523922. Its totient is φ = 643523920.

The previous prime is 643523897. The next prime is 643523929. The reversal of 643523921 is 129325346.

643523921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 622003600 + 21520321 = 24940^2 + 4639^2 .

It is a cyclic number.

It is not a de Polignac number, because 643523921 - 2¹⁰ = 643522897 is a prime.

It is not a weakly prime, because it can be changed into another prime (643523929) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321761960 + 321761961.

It is an arithmetic number, because the mean of its divisors is an integer number (321761961).

Almost surely, 2^643523921 is an apocalyptic number.

It is an amenable number.

643523921 is a deficient number, since it is larger than the sum of its proper divisors (1).

643523921 is an equidigital number, since it uses as much as digits as its factorization.

643523921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 38880, while the sum is 35.

The square root of 643523921 is about 25367.7732763441. The cubic root of 643523921 is about 863.3526605626.

The spelling of 643523921 in words is "six hundred forty-three million, five hundred twenty-three thousand, nine hundred twenty-one".