66851821 has 2 divisors, whose sum is σ = 66851822. Its totient is φ = 66851820.

The previous prime is 66851819. The next prime is 66851833. The reversal of 66851821 is 12815866.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 48024900 + 18826921 = 6930^2 + 4339^2 .

It is a cyclic number.

It is not a de Polignac number, because 66851821 - 2¹ = 66851819 is a prime.

Together with 66851819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66851881) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33425910 + 33425911.

It is an arithmetic number, because the mean of its divisors is an integer number (33425911).

Almost surely, 2^66851821 is an apocalyptic number.

It is an amenable number.

66851821 is a deficient number, since it is larger than the sum of its proper divisors (1).

66851821 is an equidigital number, since it uses as much as digits as its factorization.

66851821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 23040, while the sum is 37.

The square root of 66851821 is about 8176.2962886627. The cubic root of 66851821 is about 405.8551680740.

The spelling of 66851821 in words is "sixty-six million, eight hundred fifty-one thousand, eight hundred twenty-one".