172118021 has 4 divisors (see below), whose sum is σ = 172237932. Its totient is φ = 171998112.

The previous prime is 172117991. The next prime is 172118029. The reversal of 172118021 is 120811271.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 120811271 = 7 ⋅17258753.

It can be written as a sum of positive squares in 2 ways, for example, as 170015521 + 2102500 = 13039^2 + 1450^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-172118021 is a prime.

It is a super-2 number, since 2×172118021² = 59249226305912882, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (172118029) 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, 57776 + ... + 60681.

It is an arithmetic number, because the mean of its divisors is an integer number (43059483).

Almost surely, 2^172118021 is an apocalyptic number.

It is an amenable number.

172118021 is a deficient number, since it is larger than the sum of its proper divisors (119911).

172118021 is a wasteful number, since it uses less digits than its factorization.

172118021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 119910.

The product of its (nonzero) digits is 224, while the sum is 23.

The square root of 172118021 is about 13119.3757854556. The cubic root of 172118021 is about 556.2569471674.

Adding to 172118021 its reverse (120811271), we get a palindrome (292929292).

The spelling of 172118021 in words is "one hundred seventy-two million, one hundred eighteen thousand, twenty-one".