643900637509 has 2 divisors, whose sum is σ = 643900637510. Its totient is φ = 643900637508.

The previous prime is 643900637507. The next prime is 643900637531. The reversal of 643900637509 is 905736009346.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 362897808100 + 281002829409 = 602410^2 + 530097^2 .

It is a cyclic number.

It is not a de Polignac number, because 643900637509 - 2¹ = 643900637507 is a prime.

Together with 643900637507, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (643900637507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321950318754 + 321950318755.

It is an arithmetic number, because the mean of its divisors is an integer number (321950318755).

Almost surely, 2^643900637509 is an apocalyptic number.

It is an amenable number.

643900637509 is a deficient number, since it is larger than the sum of its proper divisors (1).

643900637509 is an equidigital number, since it uses as much as digits as its factorization.

643900637509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3674160, while the sum is 52.

The spelling of 643900637509 in words is "six hundred forty-three billion, nine hundred million, six hundred thirty-seven thousand, five hundred nine".