21172313 has 4 divisors (see below), whose sum is σ = 21197988. Its totient is φ = 21146640.

The previous prime is 21172309. The next prime is 21172331. The reversal of 21172313 is 31327112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1926544 + 19245769 = 1388^2 + 4387^2 .

It is a cyclic number.

It is not a de Polignac number, because 21172313 - 2² = 21172309 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21172343) 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, 11558 + ... + 13263.

It is an arithmetic number, because the mean of its divisors is an integer number (5299497).

Almost surely, 2^21172313 is an apocalyptic number.

It is an amenable number.

21172313 is a deficient number, since it is larger than the sum of its proper divisors (25675).

21172313 is an equidigital number, since it uses as much as digits as its factorization.

21172313 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25674.

The product of its digits is 252, while the sum is 20.

The square root of 21172313 is about 4601.3381749226. The cubic root of 21172313 is about 276.6449638627.

Adding to 21172313 its reverse (31327112), we get a palindrome (52499425).

The spelling of 21172313 in words is "twenty-one million, one hundred seventy-two thousand, three hundred thirteen".