66549336721 has 6 divisors (see below), whose sum is σ = 77414534610. Its totient is φ = 57042288576.

The previous prime is 66549336719. The next prime is 66549336767. The reversal of 66549336721 is 12763394566.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 55078926721 + 11470410000 = 234689^2 + 107100^2 .

It is not a de Polignac number, because 66549336721 - 2¹ = 66549336719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (66549331721) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 679074816 + ... + 679074913.

It is an arithmetic number, because the mean of its divisors is an integer number (12902422435).

Almost surely, 2^66549336721 is an apocalyptic number.

It is an amenable number.

66549336721 is a deficient number, since it is larger than the sum of its proper divisors (10865197889).

66549336721 is a wasteful number, since it uses less digits than its factorization.

66549336721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1358149743 (or 1358149736 counting only the distinct ones).

The product of its digits is 4898880, while the sum is 52.

The spelling of 66549336721 in words is "sixty-six billion, five hundred forty-nine million, three hundred thirty-six thousand, seven hundred twenty-one".