215561 has 4 divisors (see below), whose sum is σ = 217092. Its totient is φ = 214032.

The previous prime is 215531. The next prime is 215563. The reversal of 215561 is 165512.

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 156025 + 59536 = 395^2 + 244^2 .

It is a cyclic number.

It is not a de Polignac number, because 215561 - 2⁶ = 215497 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 (215563) 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 3 ways as a sum of consecutive naturals, for example, 530 + ... + 843.

It is an arithmetic number, because the mean of its divisors is an integer number (54273).

2²¹⁵⁵⁶¹ is an apocalyptic number.

It is an amenable number.

215561 is a deficient number, since it is larger than the sum of its proper divisors (1531).

215561 is a wasteful number, since it uses less digits than its factorization.

215561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1530.

The product of its digits is 300, while the sum is 20.

The square root of 215561 is about 464.2854725274. The cubic root of 215561 is about 59.9593242829.

The spelling of 215561 in words is "two hundred fifteen thousand, five hundred sixty-one".