172187721 has 8 divisors (see below), whose sum is σ = 255092960. Its totient is φ = 114791796.

The previous prime is 172187693. The next prime is 172187731. The reversal of 172187721 is 127781271.

It is not a de Polignac number, because 172187721 - 2⁶ = 172187657 is a prime.

It is a super-2 number, since 2×172187721² = 59297222526347682, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (172187731) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3188635 + ... + 3188688.

It is an arithmetic number, because the mean of its divisors is an integer number (31886620).

Almost surely, 2^172187721 is an apocalyptic number.

It is an amenable number.

172187721 is a deficient number, since it is larger than the sum of its proper divisors (82905239).

172187721 is an equidigital number, since it uses as much as digits as its factorization.

172187721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6377332 (or 6377326 counting only the distinct ones).

The product of its digits is 10976, while the sum is 36.

The square root of 172187721 is about 13122.0318929654. The cubic root of 172187721 is about 556.3320233208.

The spelling of 172187721 in words is "one hundred seventy-two million, one hundred eighty-seven thousand, seven hundred twenty-one".