66821 has 2 divisors, whose sum is σ = 66822. Its totient is φ = 66820.

The previous prime is 66809. The next prime is 66841. The reversal of 66821 is 12866.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 45796 + 21025 = 214^2 + 145^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66821 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66841) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33410 + 33411.

It is an arithmetic number, because the mean of its divisors is an integer number (33411).

2⁶⁶⁸²¹ is an apocalyptic number.

It is an amenable number.

66821 is a deficient number, since it is larger than the sum of its proper divisors (1).

66821 is an equidigital number, since it uses as much as digits as its factorization.

66821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 576, while the sum is 23.

The square root of 66821 is about 258.4975821937. The cubic root of 66821 is about 40.5792787400.

It can be divided in two parts, 668 and 21, that multiplied together give a triangular number (14028 = T₁₆₇).

The spelling of 66821 in words is "sixty-six thousand, eight hundred twenty-one".