645683021 has 4 divisors (see below), whose sum is σ = 645738012. Its totient is φ = 645628032.

The previous prime is 645682993. The next prime is 645683033. The reversal of 645683021 is 120386546.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 382789225 + 262893796 = 19565^2 + 16214^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-645683021 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645683081) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2006 + ... + 35991.

It is an arithmetic number, because the mean of its divisors is an integer number (161434503).

Almost surely, 2^645683021 is an apocalyptic number.

It is an amenable number.

645683021 is a deficient number, since it is larger than the sum of its proper divisors (54991).

645683021 is a wasteful number, since it uses less digits than its factorization.

645683021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 54990.

The product of its (nonzero) digits is 34560, while the sum is 35.

The square root of 645683021 is about 25410.2936031837. The cubic root of 645683021 is about 864.3171333276.

The spelling of 645683021 in words is "six hundred forty-five million, six hundred eighty-three thousand, twenty-one".