66821856 has 24 divisors (see below), whose sum is σ = 175407624. Its totient is φ = 22273920.

The previous prime is 66821851. The next prime is 66821857. The reversal of 66821856 is 65812866.

It is a tau number, because it is divible by the number of its divisors (24).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66821851) 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 in 3 ways as a sum of consecutive naturals, for example, 347935 + ... + 348126.

It is an arithmetic number, because the mean of its divisors is an integer number (7308651).

Almost surely, 2^66821856 is an apocalyptic number.

It is an amenable number.

66821856 is an abundant number, since it is smaller than the sum of its proper divisors (108585768).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

66821856 is a wasteful number, since it uses less digits than its factorization.

66821856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 696074 (or 696066 counting only the distinct ones).

The product of its digits is 138240, while the sum is 42.

The square root of 66821856 is about 8174.4636521303. The cubic root of 66821856 is about 405.7945201743.

The spelling of 66821856 in words is "sixty-six million, eight hundred twenty-one thousand, eight hundred fifty-six".