640621649 has 2 divisors, whose sum is σ = 640621650. Its totient is φ = 640621648.

The previous prime is 640621643. The next prime is 640621669. The reversal of 640621649 is 946126046.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 491952400 + 148669249 = 22180^2 + 12193^2 .

It is a cyclic number.

It is not a de Polignac number, because 640621649 - 2⁴ = 640621633 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (640621643) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320310824 + 320310825.

It is an arithmetic number, because the mean of its divisors is an integer number (320310825).

Almost surely, 2^640621649 is an apocalyptic number.

It is an amenable number.

640621649 is a deficient number, since it is larger than the sum of its proper divisors (1).

640621649 is an equidigital number, since it uses as much as digits as its factorization.

640621649 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 62208, while the sum is 38.

The square root of 640621649 is about 25310.5047164216. The cubic root of 640621649 is about 862.0528070068.

The spelling of 640621649 in words is "six hundred forty million, six hundred twenty-one thousand, six hundred forty-nine".