405661 has 4 divisors (see below), whose sum is σ = 411292. Its totient is φ = 400032.

The previous prime is 405659. The next prime is 405667. The reversal of 405661 is 166504.

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 319225 + 86436 = 565^2 + 294^2 .

It is a cyclic number.

It is not a de Polignac number, because 405661 - 2¹ = 405659 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 (405667) 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, 2706 + ... + 2851.

It is an arithmetic number, because the mean of its divisors is an integer number (102823).

2⁴⁰⁵⁶⁶¹ is an apocalyptic number.

It is an amenable number.

405661 is a deficient number, since it is larger than the sum of its proper divisors (5631).

405661 is an equidigital number, since it uses as much as digits as its factorization.

405661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5630.

The product of its (nonzero) digits is 720, while the sum is 22.

The square root of 405661 is about 636.9152219880. The cubic root of 405661 is about 74.0265913687.

The spelling of 405661 in words is "four hundred five thousand, six hundred sixty-one".