215861 has 4 divisors (see below), whose sum is σ = 218892. Its totient is φ = 212832.

The previous prime is 215857. The next prime is 215863. The reversal of 215861 is 168512.

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 78961 + 136900 = 281^2 + 370^2 .

It is a cyclic number.

It is not a de Polignac number, because 215861 - 2² = 215857 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 215861.

It is not an unprimeable number, because it can be changed into a prime (215863) 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, 1406 + ... + 1551.

It is an arithmetic number, because the mean of its divisors is an integer number (54723).

2²¹⁵⁸⁶¹ is an apocalyptic number.

It is an amenable number.

215861 is a deficient number, since it is larger than the sum of its proper divisors (3031).

215861 is an equidigital number, since it uses as much as digits as its factorization.

215861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3030.

The product of its digits is 480, while the sum is 23.

The square root of 215861 is about 464.6084372889. The cubic root of 215861 is about 59.9871268679.

The spelling of 215861 in words is "two hundred fifteen thousand, eight hundred sixty-one".