661665 has 8 divisors (see below), whose sum is σ = 1058688. Its totient is φ = 352880.

The previous prime is 661663. The next prime is 661673. The reversal of 661665 is 566166.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 661665 - 2¹ = 661663 is a prime.

It is not an unprimeable number, because it can be changed into a prime (661663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 22041 + ... + 22070.

It is an arithmetic number, because the mean of its divisors is an integer number (132336).

2⁶⁶¹⁶⁶⁵ is an apocalyptic number.

It is an amenable number.

661665 is a deficient number, since it is larger than the sum of its proper divisors (397023).

661665 is a wasteful number, since it uses less digits than its factorization.

661665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44119.

The product of its digits is 6480, while the sum is 30.

The square root of 661665 is about 813.4279316571. The cubic root of 661665 is about 87.1390299186.

It can be divided in two parts, 661 and 665, that added together give a triangular number (1326 = T₅₁).

The spelling of 661665 in words is "six hundred sixty-one thousand, six hundred sixty-five".