21172117 has 12 divisors (see below), whose sum is σ = 22368420. Its totient is φ = 20014848.

The previous prime is 21172097. The next prime is 21172133. The reversal of 21172117 is 71127112.

It can be written as a sum of positive squares in 6 ways, for example, as 323761 + 20848356 = 569^2 + 4566^2 .

It is not a de Polignac number, because 21172117 - 2⁷ = 21171989 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21172147) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 154473 + ... + 154609.

It is an arithmetic number, because the mean of its divisors is an integer number (1864035).

Almost surely, 2^21172117 is an apocalyptic number.

It is an amenable number.

21172117 is a deficient number, since it is larger than the sum of its proper divisors (1196303).

21172117 is an equidigital number, since it uses as much as digits as its factorization.

21172117 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 312 (or 239 counting only the distinct ones).

The product of its digits is 196, while the sum is 22.

The square root of 21172117 is about 4601.3168767213. The cubic root of 21172117 is about 276.6441101915.

Adding to 21172117 its reverse (71127112), we get a palindrome (92299229).

The spelling of 21172117 in words is "twenty-one million, one hundred seventy-two thousand, one hundred seventeen".