866221 has 2 divisors, whose sum is σ = 866222. Its totient is φ = 866220.

The previous prime is 866213. The next prime is 866231. The reversal of 866221 is 122668.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 784996 + 81225 = 886^2 + 285^2 .

It is a cyclic number.

It is not a de Polignac number, because 866221 - 2³ = 866213 is a prime.

It is an Ulam number.

866221 is a lucky number.

It is a nialpdrome in base 10.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (866231) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 433110 + 433111.

It is an arithmetic number, because the mean of its divisors is an integer number (433111).

2⁸⁶⁶²²¹ is an apocalyptic number.

It is an amenable number.

866221 is a deficient number, since it is larger than the sum of its proper divisors (1).

866221 is an equidigital number, since it uses as much as digits as its factorization.

866221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1152, while the sum is 25.

The square root of 866221 is about 930.7099440750. The cubic root of 866221 is about 95.3256048092.

Adding to 866221 its reverse (122668), we get a palindrome (988889).

The spelling of 866221 in words is "eight hundred sixty-six thousand, two hundred twenty-one".