66721680 has 60 divisors (see below), whose sum is σ = 224076060. Its totient is φ = 17792256.

The previous prime is 66721679. The next prime is 66721687. The reversal of 66721680 is 8612766.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 19607184 + 47114496 = 4428^2 + 6864^2 .

It is a tau number, because it is divible by the number of its divisors (60).

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 (66721687) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 45615 + ... + 47054.

It is an arithmetic number, because the mean of its divisors is an integer number (3734601).

Almost surely, 2^66721680 is an apocalyptic number.

66721680 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

66721680 is an abundant number, since it is smaller than the sum of its proper divisors (157354380).

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

66721680 is a wasteful number, since it uses less digits than its factorization.

66721680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 92688 (or 92679 counting only the distinct ones).

The product of its (nonzero) digits is 24192, while the sum is 36.

The square root of 66721680 is about 8168.3339794599. Note that the first 3 decimals coincide. The cubic root of 66721680 is about 405.5916364416.

The spelling of 66721680 in words is "sixty-six million, seven hundred twenty-one thousand, six hundred eighty".