13166645721 has 4 divisors (see below), whose sum is σ = 17555527632. Its totient is φ = 8777763812.

The previous prime is 13166645677. The next prime is 13166645731. The reversal of 13166645721 is 12754666131.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12754666131 = 3 ⋅4251555377.

It is a cyclic number.

It is not a de Polignac number, because 13166645721 - 2¹⁰ = 13166644697 is a prime.

It is not an unprimeable number, because it can be changed into a prime (13166645731) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2194440951 + ... + 2194440956.

It is an arithmetic number, because the mean of its divisors is an integer number (4388881908).

Almost surely, 2^13166645721 is an apocalyptic number.

It is an amenable number.

13166645721 is a deficient number, since it is larger than the sum of its proper divisors (4388881911).

13166645721 is an equidigital number, since it uses as much as digits as its factorization.

13166645721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4388881910.

The product of its digits is 181440, while the sum is 42.

The spelling of 13166645721 in words is "thirteen billion, one hundred sixty-six million, six hundred forty-five thousand, seven hundred twenty-one".