215921 has 2 divisors, whose sum is σ = 215922. Its totient is φ = 215920.

The previous prime is 215909. The next prime is 215927. The reversal of 215921 is 129512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 215296 + 625 = 464^2 + 25^2 .

It is a cyclic number.

It is not a de Polignac number, because 215921 - 2⁶ = 215857 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 215893 and 215902.

It is not a weakly prime, because it can be changed into another prime (215927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 107960 + 107961.

It is an arithmetic number, because the mean of its divisors is an integer number (107961).

2²¹⁵⁹²¹ is an apocalyptic number.

It is an amenable number.

215921 is a deficient number, since it is larger than the sum of its proper divisors (1).

215921 is an equidigital number, since it uses as much as digits as its factorization.

215921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 180, while the sum is 20.

The square root of 215921 is about 464.6730033045. The cubic root of 215921 is about 59.9926842932.

The spelling of 215921 in words is "two hundred fifteen thousand, nine hundred twenty-one".