661845 has 8 divisors (see below), whose sum is σ = 1058976. Its totient is φ = 352976.

The previous prime is 661823. The next prime is 661849. The reversal of 661845 is 548166.

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 661845 - 2¹⁷ = 530773 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661849) 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, 22047 + ... + 22076.

It is an arithmetic number, because the mean of its divisors is an integer number (132372).

2⁶⁶¹⁸⁴⁵ is an apocalyptic number.

It is an amenable number.

661845 is a deficient number, since it is larger than the sum of its proper divisors (397131).

661845 is a wasteful number, since it uses less digits than its factorization.

661845 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44131.

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

The square root of 661845 is about 813.5385670022. The cubic root of 661845 is about 87.1469309980.

Subtracting from 661845 its product of digits (5760), we obtain a triangular number (656085 = T₁₁₄₅).

The spelling of 661845 in words is "six hundred sixty-one thousand, eight hundred forty-five".