215665 has 4 divisors (see below), whose sum is σ = 258804. Its totient is φ = 172528.

The previous prime is 215659. The next prime is 215681. The reversal of 215665 is 566512.

215665 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 can be written as a sum of positive squares in 2 ways, for example, as 62001 + 153664 = 249^2 + 392^2 .

It is a cyclic number.

It is not a de Polignac number, because 215665 - 2⁹ = 215153 is a prime.

It is a super-2 number, since 2×215665² = 93022784450, which contains 22 as substring.

It is a Duffinian number.

215665 is a lucky number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21562 + ... + 21571.

It is an arithmetic number, because the mean of its divisors is an integer number (64701).

2²¹⁵⁶⁶⁵ is an apocalyptic number.

It is an amenable number.

215665 is a deficient number, since it is larger than the sum of its proper divisors (43139).

215665 is an equidigital number, since it uses as much as digits as its factorization.

215665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43138.

The product of its digits is 1800, while the sum is 25.

The square root of 215665 is about 464.3974590800. The cubic root of 215665 is about 59.9689654318.

The spelling of 215665 in words is "two hundred fifteen thousand, six hundred sixty-five".