266821 has 2 divisors, whose sum is σ = 266822. Its totient is φ = 266820.

The previous prime is 266801. The next prime is 266837. The reversal of 266821 is 128662.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 236196 + 30625 = 486^2 + 175^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-266821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (266801) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 133410 + 133411.

It is an arithmetic number, because the mean of its divisors is an integer number (133411).

2²⁶⁶⁸²¹ is an apocalyptic number.

It is an amenable number.

266821 is a deficient number, since it is larger than the sum of its proper divisors (1).

266821 is an equidigital number, since it uses as much as digits as its factorization.

266821 is an evil number, because the sum of its binary digits is even.

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

The square root of 266821 is about 516.5471904870. The cubic root of 266821 is about 64.3783738452.

The spelling of 266821 in words is "two hundred sixty-six thousand, eight hundred twenty-one".