215665561 has 16 divisors (see below), whose sum is σ = 231860160. Its totient is φ = 199990080.

The previous prime is 215665531. The next prime is 215665573. The reversal of 215665561 is 165566512.

It is a cyclic number.

It is not a de Polignac number, because 215665561 - 2⁵ = 215665529 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 215665561.

It is not an unprimeable number, because it can be changed into a prime (215665501) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 367110 + ... + 367696.

It is an arithmetic number, because the mean of its divisors is an integer number (14491260).

Almost surely, 2^215665561 is an apocalyptic number.

It is an amenable number.

215665561 is a deficient number, since it is larger than the sum of its proper divisors (16194599).

215665561 is a wasteful number, since it uses less digits than its factorization.

215665561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 984.

The product of its digits is 54000, while the sum is 37.

The square root of 215665561 is about 14685.5562032904. The cubic root of 215665561 is about 599.6901743002.

The spelling of 215665561 in words is "two hundred fifteen million, six hundred sixty-five thousand, five hundred sixty-one".