645681 has 8 divisors (see below), whose sum is σ = 867744. Its totient is φ = 427040.

The previous prime is 645661. The next prime is 645683. The reversal of 645681 is 186546.

645681 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It is a cyclic number.

It is not a de Polignac number, because 645681 - 2⁵ = 645649 is a prime.

It is a super-2 number, since 2×645681² = 833807907522, which contains 22 as substring.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 645681.

It is not an unprimeable number, because it can be changed into a prime (645683) 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, 375 + ... + 1196.

It is an arithmetic number, because the mean of its divisors is an integer number (108468).

2⁶⁴⁵⁶⁸¹ is an apocalyptic number.

It is an amenable number.

645681 is a deficient number, since it is larger than the sum of its proper divisors (222063).

645681 is a wasteful number, since it uses less digits than its factorization.

645681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1711.

The product of its digits is 5760, while the sum is 30.

The square root of 645681 is about 803.5427804417. The cubic root of 645681 is about 86.4316231550.

It can be divided in two parts, 645 and 681, that added together give a triangular number (1326 = T₅₁).

The spelling of 645681 in words is "six hundred forty-five thousand, six hundred eighty-one".