21172919 has 4 divisors (see below), whose sum is σ = 21214080. Its totient is φ = 21131760.

The previous prime is 21172913. The next prime is 21172927. The reversal of 21172919 is 91927112.

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

It is not a de Polignac number, because 21172919 - 2⁸ = 21172663 is a prime.

It is a super-2 number, since 2×21172919² = 896584997961122, 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 (21172913) 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, 19799 + ... + 20840.

It is an arithmetic number, because the mean of its divisors is an integer number (5303520).

Almost surely, 2^21172919 is an apocalyptic number.

21172919 is a deficient number, since it is larger than the sum of its proper divisors (41161).

21172919 is an equidigital number, since it uses as much as digits as its factorization.

21172919 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 41160.

The product of its digits is 2268, while the sum is 32.

The square root of 21172919 is about 4601.4040248602. The cubic root of 21172919 is about 276.6476032413.

The spelling of 21172919 in words is "twenty-one million, one hundred seventy-two thousand, nine hundred nineteen".