681645 has 16 divisors (see below), whose sum is σ = 1128960. Its totient is φ = 350784.

The previous prime is 681631. The next prime is 681647. The reversal of 681645 is 546186.

It is not a de Polignac number, because 681645 - 2⁵ = 681613 is a prime.

It is a super-3 number, since 3×681645³ = 950158406227233375, which contains 333 as substring.

681645 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (681647) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 349 + ... + 1218.

It is an arithmetic number, because the mean of its divisors is an integer number (70560).

2⁶⁸¹⁶⁴⁵ is an apocalyptic number.

It is an amenable number.

681645 is a deficient number, since it is larger than the sum of its proper divisors (447315).

681645 is a wasteful number, since it uses less digits than its factorization.

681645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1604.

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

The square root of 681645 is about 825.6179503863. The cubic root of 681645 is about 88.0074459953.

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

The spelling of 681645 in words is "six hundred eighty-one thousand, six hundred forty-five".