643967993 has 2 divisors, whose sum is σ = 643967994. Its totient is φ = 643967992.

The previous prime is 643967953. The next prime is 643968001. The reversal of 643967993 is 399769346.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 617671609 + 26296384 = 24853^2 + 5128^2 .

It is a cyclic number.

It is not a de Polignac number, because 643967993 - 2¹⁸ = 643705849 is a prime.

It is not a weakly prime, because it can be changed into another prime (643967953) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321983996 + 321983997.

It is an arithmetic number, because the mean of its divisors is an integer number (321983997).

Almost surely, 2^643967993 is an apocalyptic number.

It is an amenable number.

643967993 is a deficient number, since it is larger than the sum of its proper divisors (1).

643967993 is an equidigital number, since it uses as much as digits as its factorization.

643967993 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6613488, while the sum is 56.

The square root of 643967993 is about 25376.5244468190. The cubic root of 643967993 is about 863.5512041215.

The spelling of 643967993 in words is "six hundred forty-three million, nine hundred sixty-seven thousand, nine hundred ninety-three".