643721399 has 2 divisors, whose sum is σ = 643721400. Its totient is φ = 643721398.

The previous prime is 643721369. The next prime is 643721413. The reversal of 643721399 is 993127346.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 643721399 - 2²⁴ = 626944183 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (643721339) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321860699 + 321860700.

It is an arithmetic number, because the mean of its divisors is an integer number (321860700).

Almost surely, 2^643721399 is an apocalyptic number.

643721399 is a deficient number, since it is larger than the sum of its proper divisors (1).

643721399 is an equidigital number, since it uses as much as digits as its factorization.

643721399 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 244944, while the sum is 44.

The square root of 643721399 is about 25371.6652784164. The cubic root of 643721399 is about 863.4409637913.

The spelling of 643721399 in words is "six hundred forty-three million, seven hundred twenty-one thousand, three hundred ninety-nine".