645996391 has 4 divisors (see below), whose sum is σ = 646062912. Its totient is φ = 645929872.

The previous prime is 645996389. The next prime is 645996397. The reversal of 645996391 is 193699546.

645996391 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 is a cyclic number.

It is not a de Polignac number, because 645996391 - 2¹ = 645996389 is a prime.

It is a super-2 number, since 2×645996391² = 834622674370049762, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645996397) 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, 15550 + ... + 39163.

It is an arithmetic number, because the mean of its divisors is an integer number (161515728).

Almost surely, 2^645996391 is an apocalyptic number.

645996391 is a deficient number, since it is larger than the sum of its proper divisors (66521).

645996391 is a wasteful number, since it uses less digits than its factorization.

645996391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 66520.

The product of its digits is 1574640, while the sum is 52.

The square root of 645996391 is about 25416.4590570756. The cubic root of 645996391 is about 864.4569373519.

The spelling of 645996391 in words is "six hundred forty-five million, nine hundred ninety-six thousand, three hundred ninety-one".