681638 has 4 divisors (see below), whose sum is σ = 1022460. Its totient is φ = 340818.

The previous prime is 681631. The next prime is 681647. The reversal of 681638 is 836186.

Added to its reverse (836186) it gives a square (1517824 = 1232²).

681638 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.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (681631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 170408 + ... + 170411.

It is an arithmetic number, because the mean of its divisors is an integer number (255615).

681638 is a Friedman number, since it can be written as 166+88^3, using all its digits and the basic arithmetic operations.

2⁶⁸¹⁶³⁸ is an apocalyptic number.

681638 is a deficient number, since it is larger than the sum of its proper divisors (340822).

681638 is a wasteful number, since it uses less digits than its factorization.

681638 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 340821.

The product of its digits is 6912, while the sum is 32.

The square root of 681638 is about 825.6137111265. The cubic root of 681638 is about 88.0071447367.

Adding to 681638 its reverse (836186), we get a square (1517824 = 1232²).

The spelling of 681638 in words is "six hundred eighty-one thousand, six hundred thirty-eight".