640355897 has 2 divisors, whose sum is σ = 640355898. Its totient is φ = 640355896.

The previous prime is 640355869. The next prime is 640355899. The reversal of 640355897 is 798553046.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 640140601 + 215296 = 25301^2 + 464^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640355897 is a prime.

Together with 640355899, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (640355899) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320177948 + 320177949.

It is an arithmetic number, because the mean of its divisors is an integer number (320177949).

Almost surely, 2^640355897 is an apocalyptic number.

It is an amenable number.

640355897 is a deficient number, since it is larger than the sum of its proper divisors (1).

640355897 is an equidigital number, since it uses as much as digits as its factorization.

640355897 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 907200, while the sum is 47.

The square root of 640355897 is about 25305.2543358094. The cubic root of 640355897 is about 861.9335874208.

The spelling of 640355897 in words is "six hundred forty million, three hundred fifty-five thousand, eight hundred ninety-seven".