66818821 has 4 divisors (see below), whose sum is σ = 67410252. Its totient is φ = 66227392.

The previous prime is 66818809. The next prime is 66818831. The reversal of 66818821 is 12881866.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12881866 = 2 ⋅6440933.

It can be written as a sum of positive squares in 2 ways, for example, as 24750625 + 42068196 = 4975^2 + 6486^2 .

It is a cyclic number.

It is not a de Polignac number, because 66818821 - 2⁷ = 66818693 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66818831) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 295546 + ... + 295771.

It is an arithmetic number, because the mean of its divisors is an integer number (16852563).

Almost surely, 2^66818821 is an apocalyptic number.

It is an amenable number.

66818821 is a deficient number, since it is larger than the sum of its proper divisors (591431).

66818821 is a wasteful number, since it uses less digits than its factorization.

66818821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 591430.

The product of its digits is 36864, while the sum is 40.

The square root of 66818821 is about 8174.2780109316. The cubic root of 66818821 is about 405.7883764508.

The spelling of 66818821 in words is "sixty-six million, eight hundred eighteen thousand, eight hundred twenty-one".