645855981 has 8 divisors (see below), whose sum is σ = 861633024. Its totient is φ = 430324800.

The previous prime is 645855971. The next prime is 645855989. The reversal of 645855981 is 189558546.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 645855981 - 2⁷ = 645855853 is a prime.

It is a super-2 number, since 2×645855981² = 834259896386944722, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645855989) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 55245 + ... + 65906.

It is an arithmetic number, because the mean of its divisors is an integer number (107704128).

Almost surely, 2^645855981 is an apocalyptic number.

It is an amenable number.

645855981 is a deficient number, since it is larger than the sum of its proper divisors (215777043).

645855981 is a wasteful number, since it uses less digits than its factorization.

645855981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 122931.

The product of its digits is 1728000, while the sum is 51.

The square root of 645855981 is about 25413.6967204695. The cubic root of 645855981 is about 864.3943017112.

The spelling of 645855981 in words is "six hundred forty-five million, eight hundred fifty-five thousand, nine hundred eighty-one".