643928531 has 2 divisors, whose sum is σ = 643928532. Its totient is φ = 643928530.

The previous prime is 643928513. The next prime is 643928561. The reversal of 643928531 is 135829346.

Together with previous prime (643928513) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643928531 is a prime.

It is a super-2 number, since 2×643928531² = 829287906071635922, which contains 22 as substring.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (643928561) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321964265 + 321964266.

It is an arithmetic number, because the mean of its divisors is an integer number (321964266).

Almost surely, 2^643928531 is an apocalyptic number.

643928531 is a deficient number, since it is larger than the sum of its proper divisors (1).

643928531 is an equidigital number, since it uses as much as digits as its factorization.

643928531 is an evil number, because the sum of its binary digits is even.

The product of its digits is 155520, while the sum is 41.

The square root of 643928531 is about 25375.7469052637. The cubic root of 643928531 is about 863.5335644489.

The spelling of 643928531 in words is "six hundred forty-three million, nine hundred twenty-eight thousand, five hundred thirty-one".