645687881 has 4 divisors (see below), whose sum is σ = 648143232. Its totient is φ = 643232532.

The previous prime is 645687877. The next prime is 645687883. The reversal of 645687881 is 188786546.

645687881 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 Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 645687881 - 2² = 645687877 is a prime.

It is a super-2 number, since 2×645687881² = 833825679340540322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (645687883) 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, 1227281 + ... + 1227806.

It is an arithmetic number, because the mean of its divisors is an integer number (162035808).

Almost surely, 2^645687881 is an apocalyptic number.

It is an amenable number.

645687881 is a deficient number, since it is larger than the sum of its proper divisors (2455351).

645687881 is a wasteful number, since it uses less digits than its factorization.

645687881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2455350.

The product of its digits is 2580480, while the sum is 53.

The square root of 645687881 is about 25410.3892335399. The cubic root of 645687881 is about 864.3193018688.

The spelling of 645687881 in words is "six hundred forty-five million, six hundred eighty-seven thousand, eight hundred eighty-one".