645093721 has 4 divisors (see below), whose sum is σ = 645456100. Its totient is φ = 644731344.

The previous prime is 645093707. The next prime is 645093739. The reversal of 645093721 is 127390546.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 393427225 + 251666496 = 19835^2 + 15864^2 .

It is a cyclic number.

It is not a de Polignac number, because 645093721 - 2⁹ = 645093209 is a prime.

It is a super-3 number, since 3×645093721³ (a number of 27 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (645093751) 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, 178506 + ... + 182083.

It is an arithmetic number, because the mean of its divisors is an integer number (161364025).

Almost surely, 2^645093721 is an apocalyptic number.

It is an amenable number.

645093721 is a deficient number, since it is larger than the sum of its proper divisors (362379).

645093721 is a wasteful number, since it uses less digits than its factorization.

645093721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 362378.

The product of its (nonzero) digits is 45360, while the sum is 37.

The square root of 645093721 is about 25398.6952617649. The cubic root of 645093721 is about 864.0541058545.

The spelling of 645093721 in words is "six hundred forty-five million, ninety-three thousand, seven hundred twenty-one".