645390689 has 4 divisors (see below), whose sum is σ = 679358640. Its totient is φ = 611422740.

The previous prime is 645390673. The next prime is 645390701. The reversal of 645390689 is 986093546.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 986093546 = 2 ⋅493046773.

It is a cyclic number.

It is not a de Polignac number, because 645390689 - 2⁴ = 645390673 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (645390589) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16983947 + ... + 16983984.

It is an arithmetic number, because the mean of its divisors is an integer number (169839660).

Almost surely, 2^645390689 is an apocalyptic number.

It is an amenable number.

645390689 is a deficient number, since it is larger than the sum of its proper divisors (33967951).

645390689 is a wasteful number, since it uses less digits than its factorization.

645390689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33967950.

The product of its (nonzero) digits is 1399680, while the sum is 50.

The square root of 645390689 is about 25404.5407161791. The cubic root of 645390689 is about 864.1866742172.

The spelling of 645390689 in words is "six hundred forty-five million, three hundred ninety thousand, six hundred eighty-nine".