643954709 has 2 divisors, whose sum is σ = 643954710. Its totient is φ = 643954708.

The previous prime is 643954693. The next prime is 643954721. The reversal of 643954709 is 907459346.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 563350225 + 80604484 = 23735^2 + 8978^2 .

It is a cyclic number.

It is not a de Polignac number, because 643954709 - 2⁴ = 643954693 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (643954769) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321977354 + 321977355.

It is an arithmetic number, because the mean of its divisors is an integer number (321977355).

Almost surely, 2^643954709 is an apocalyptic number.

It is an amenable number.

643954709 is a deficient number, since it is larger than the sum of its proper divisors (1).

643954709 is an equidigital number, since it uses as much as digits as its factorization.

643954709 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 816480, while the sum is 47.

The square root of 643954709 is about 25376.2627074989. The cubic root of 643954709 is about 863.5452662006.

The spelling of 643954709 in words is "six hundred forty-three million, nine hundred fifty-four thousand, seven hundred nine".