643918193 has 2 divisors, whose sum is σ = 643918194. Its totient is φ = 643918192.

The previous prime is 643918169. The next prime is 643918201. The reversal of 643918193 is 391819346.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 565631089 + 78287104 = 23783^2 + 8848^2 .

It is a cyclic number.

It is not a de Polignac number, because 643918193 - 2¹² = 643914097 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (643918103) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321959096 + 321959097.

It is an arithmetic number, because the mean of its divisors is an integer number (321959097).

Almost surely, 2^643918193 is an apocalyptic number.

It is an amenable number.

643918193 is a deficient number, since it is larger than the sum of its proper divisors (1).

643918193 is an equidigital number, since it uses as much as digits as its factorization.

643918193 is an evil number, because the sum of its binary digits is even.

The product of its digits is 139968, while the sum is 44.

The square root of 643918193 is about 25375.5432060084. The cubic root of 643918193 is about 863.5289432022.

The spelling of 643918193 in words is "six hundred forty-three million, nine hundred eighteen thousand, one hundred ninety-three".