643440509 has 2 divisors, whose sum is σ = 643440510. Its totient is φ = 643440508.

The previous prime is 643440493. The next prime is 643440517. The reversal of 643440509 is 905044346.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 505260484 + 138180025 = 22478^2 + 11755^2 .

It is a cyclic number.

It is not a de Polignac number, because 643440509 - 2⁴ = 643440493 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 (643440569) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321720254 + 321720255.

It is an arithmetic number, because the mean of its divisors is an integer number (321720255).

Almost surely, 2^643440509 is an apocalyptic number.

It is an amenable number.

643440509 is a deficient number, since it is larger than the sum of its proper divisors (1).

643440509 is an equidigital number, since it uses as much as digits as its factorization.

643440509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 51840, while the sum is 35.

The square root of 643440509 is about 25366.1291686375. The cubic root of 643440509 is about 863.3153570626.

The spelling of 643440509 in words is "six hundred forty-three million, four hundred forty thousand, five hundred nine".