66721824 has 144 divisors (see below), whose sum is σ = 208039104. Its totient is φ = 20160000.

The previous prime is 66721819. The next prime is 66721829. The reversal of 66721824 is 42812766.

It is an interprime number because it is at equal distance from previous prime (66721819) and next prime (66721829).

It is a tau number, because it is divible by the number of its divisors (144).

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is not an unprimeable number, because it can be changed into a prime (66721829) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 265699 + ... + 265949.

It is an arithmetic number, because the mean of its divisors is an integer number (1444716).

Almost surely, 2^66721824 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 66721824, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (104019552).

66721824 is an abundant number, since it is smaller than the sum of its proper divisors (141317280).

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

66721824 is a wasteful number, since it uses less digits than its factorization.

66721824 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 351 (or 340 counting only the distinct ones).

The product of its digits is 32256, while the sum is 36.

The square root of 66721824 is about 8168.3427939821. The cubic root of 66721824 is about 405.5919282266.

The spelling of 66721824 in words is "sixty-six million, seven hundred twenty-one thousand, eight hundred twenty-four".