668561 has 4 divisors (see below), whose sum is σ = 670500. Its totient is φ = 666624.

The previous prime is 668543. The next prime is 668567. The reversal of 668561 is 165866.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 270400 + 398161 = 520^2 + 631^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-668561 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (668567) 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, 296 + ... + 1193.

It is an arithmetic number, because the mean of its divisors is an integer number (167625).

2⁶⁶⁸⁵⁶¹ is an apocalyptic number.

It is an amenable number.

668561 is a deficient number, since it is larger than the sum of its proper divisors (1939).

668561 is a wasteful number, since it uses less digits than its factorization.

668561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1938.

The product of its digits is 8640, while the sum is 32.

The square root of 668561 is about 817.6557955521. The cubic root of 668561 is about 87.4407108557.

The spelling of 668561 in words is "six hundred sixty-eight thousand, five hundred sixty-one".