66721668 has 96 divisors (see below), whose sum is σ = 179786880. Its totient is φ = 19077120.

The previous prime is 66721661. The next prime is 66721679. The reversal of 66721668 is 86612766.

It is a happy number.

It is a Smith number, since the sum of its digits (42) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (66721661) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 368538 + ... + 368718.

It is an arithmetic number, because the mean of its divisors is an integer number (1872780).

Almost surely, 2^66721668 is an apocalyptic number.

66721668 is a gapful number since it is divisible by the number (68) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 66721668, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (89893440).

66721668 is an abundant number, since it is smaller than the sum of its proper divisors (113065212).

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

66721668 is a wasteful number, since it uses less digits than its factorization.

66721668 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 357 (or 355 counting only the distinct ones).

The product of its digits is 145152, while the sum is 42.

The square root of 66721668 is about 8168.3332449160. Note that the first 3 decimals coincide. The cubic root of 66721668 is about 405.5916121261.

It can be divided in two parts, 6672 and 1668, that multiplied together give a square (11128896 = 3336²).

The spelling of 66721668 in words is "sixty-six million, seven hundred twenty-one thousand, six hundred sixty-eight".