645649 has 2 divisors, whose sum is σ = 645650. Its totient is φ = 645648.

The previous prime is 645647. The next prime is 645661. The reversal of 645649 is 946546.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 608400 + 37249 = 780^2 + 193^2 .

It is a cyclic number.

It is not a de Polignac number, because 645649 - 2¹ = 645647 is a prime.

Together with 645647, it forms a pair of twin primes.

It is an Ulam number.

It is not a weakly prime, because it can be changed into another prime (645641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322824 + 322825.

It is an arithmetic number, because the mean of its divisors is an integer number (322825).

2⁶⁴⁵⁶⁴⁹ is an apocalyptic number.

It is an amenable number.

645649 is a deficient number, since it is larger than the sum of its proper divisors (1).

645649 is an equidigital number, since it uses as much as digits as its factorization.

645649 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 25920, while the sum is 34.

The square root of 645649 is about 803.5228683740. The cubic root of 645649 is about 86.4301952788.

The spelling of 645649 in words is "six hundred forty-five thousand, six hundred forty-nine".