66138721 has 32 divisors (see below), whose sum is σ = 80110080. Its totient is φ = 54362880.

The previous prime is 66138719. The next prime is 66138757. The reversal of 66138721 is 12783166.

66138721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 66138721 - 2¹ = 66138719 is a prime.

It is a Duffinian number.

Its product of digits (12096) is a multiple of the sum of its prime divisors (144).

It is not an unprimeable number, because it can be changed into a prime (66138521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 837160 + ... + 837238.

It is an arithmetic number, because the mean of its divisors is an integer number (2503440).

Almost surely, 2^66138721 is an apocalyptic number.

It is an amenable number.

66138721 is a deficient number, since it is larger than the sum of its proper divisors (13971359).

66138721 is a wasteful number, since it uses less digits than its factorization.

66138721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 166 (or 144 counting only the distinct ones).

The product of its digits is 12096, while the sum is 34.

The square root of 66138721 is about 8132.5716105055. The cubic root of 66138721 is about 404.4069376930.

The spelling of 66138721 in words is "sixty-six million, one hundred thirty-eight thousand, seven hundred twenty-one".