640666549 has 2 divisors, whose sum is σ = 640666550. Its totient is φ = 640666548.

The previous prime is 640666547. The next prime is 640666561. The reversal of 640666549 is 945666046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 589615524 + 51051025 = 24282^2 + 7145^2 .

It is a cyclic number.

It is not a de Polignac number, because 640666549 - 2¹ = 640666547 is a prime.

Together with 640666547, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 640666499 and 640666508.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640666547) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320333274 + 320333275.

It is an arithmetic number, because the mean of its divisors is an integer number (320333275).

Almost surely, 2^640666549 is an apocalyptic number.

It is an amenable number.

640666549 is a deficient number, since it is larger than the sum of its proper divisors (1).

640666549 is an equidigital number, since it uses as much as digits as its factorization.

640666549 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 933120, while the sum is 46.

The square root of 640666549 is about 25311.3916843780. The cubic root of 640666549 is about 862.0729464379.

The spelling of 640666549 in words is "six hundred forty million, six hundred sixty-six thousand, five hundred forty-nine".