166172721 has 32 divisors (see below), whose sum is σ = 261152640. Its totient is φ = 92659200.

The previous prime is 166172717. The next prime is 166172729. The reversal of 166172721 is 127271661.

166172721 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 166172721 - 2² = 166172717 is a prime.

It is a super-2 number, since 2×166172721² = 55226746409087682, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (166172729) 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, 217981 + ... + 218741.

It is an arithmetic number, because the mean of its divisors is an integer number (8161020).

Almost surely, 2^166172721 is an apocalyptic number.

166172721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

166172721 is a deficient number, since it is larger than the sum of its proper divisors (94979919).

166172721 is a wasteful number, since it uses less digits than its factorization.

166172721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1297.

The product of its digits is 7056, while the sum is 33.

The square root of 166172721 is about 12890.7998588140. The cubic root of 166172721 is about 549.7770126364. Note that the first 3 decimals are identical.

The spelling of 166172721 in words is "one hundred sixty-six million, one hundred seventy-two thousand, seven hundred twenty-one".