645918191 has 4 divisors (see below), whose sum is σ = 646899000. Its totient is φ = 644937384.

The previous prime is 645918181. The next prime is 645918193. The reversal of 645918191 is 191819546.

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

It is a cyclic number.

It is not a de Polignac number, because 645918191 - 2²⁶ = 578809327 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 (645918193) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 489416 + ... + 490733.

It is an arithmetic number, because the mean of its divisors is an integer number (161724750).

Almost surely, 2^645918191 is an apocalyptic number.

645918191 is a deficient number, since it is larger than the sum of its proper divisors (980809).

645918191 is an equidigital number, since it uses as much as digits as its factorization.

645918191 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 980808.

The product of its digits is 77760, while the sum is 44.

The square root of 645918191 is about 25414.9206372949. The cubic root of 645918191 is about 864.4220541537.

The spelling of 645918191 in words is "six hundred forty-five million, nine hundred eighteen thousand, one hundred ninety-one".