66721 has 2 divisors, whose sum is σ = 66722. Its totient is φ = 66720.

The previous prime is 66713. The next prime is 66733. The reversal of 66721 is 12766.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 55696 + 11025 = 236^2 + 105^2 .

It is a cyclic number.

It is not a de Polignac number, because 66721 - 2³ = 66713 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 66692 and 66701.

It is not a weakly prime, because it can be changed into another prime (66701) 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, 33360 + 33361.

It is an arithmetic number, because the mean of its divisors is an integer number (33361).

2⁶⁶⁷²¹ is an apocalyptic number.

It is an amenable number.

66721 is a deficient number, since it is larger than the sum of its proper divisors (1).

66721 is an equidigital number, since it uses as much as digits as its factorization.

66721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 504, while the sum is 22.

The square root of 66721 is about 258.3040843657. The cubic root of 66721 is about 40.5590258562.

It can be divided in two parts, 66 and 721, that multiplied together give a triangular number (47586 = T₃₀₈).

The spelling of 66721 in words is "sixty-six thousand, seven hundred twenty-one".