640991249 has 2 divisors, whose sum is σ = 640991250. Its totient is φ = 640991248.

The previous prime is 640991191. The next prime is 640991251. The reversal of 640991249 is 942199046.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 406748224 + 234243025 = 20168^2 + 15305^2 .

It is a cyclic number.

It is not a de Polignac number, because 640991249 - 2⁸ = 640990993 is a prime.

Together with 640991251, 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 (640991149) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320495624 + 320495625.

It is an arithmetic number, because the mean of its divisors is an integer number (320495625).

Almost surely, 2^640991249 is an apocalyptic number.

It is an amenable number.

640991249 is a deficient number, since it is larger than the sum of its proper divisors (1).

640991249 is an equidigital number, since it uses as much as digits as its factorization.

640991249 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 139968, while the sum is 44.

The square root of 640991249 is about 25317.8049798951. The cubic root of 640991249 is about 862.2185592693.

The spelling of 640991249 in words is "six hundred forty million, nine hundred ninety-one thousand, two hundred forty-nine".