640806989 has 2 divisors, whose sum is σ = 640806990. Its totient is φ = 640806988.

The previous prime is 640806911. The next prime is 640807003. The reversal of 640806989 is 989608046.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 469458889 + 171348100 = 21667^2 + 13090^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640806989 is a prime.

It is a super-2 number, since 2×640806989² = 821267194302492242, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen 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 (640802989) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320403494 + 320403495.

It is an arithmetic number, because the mean of its divisors is an integer number (320403495).

Almost surely, 2^640806989 is an apocalyptic number.

It is an amenable number.

640806989 is a deficient number, since it is larger than the sum of its proper divisors (1).

640806989 is an equidigital number, since it uses as much as digits as its factorization.

640806989 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 746496, while the sum is 50.

The square root of 640806989 is about 25314.1657772876. The cubic root of 640806989 is about 862.1359332753.

The spelling of 640806989 in words is "six hundred forty million, eight hundred six thousand, nine hundred eighty-nine".