21105172 has 24 divisors (see below), whose sum is σ = 41594112. Its totient is φ = 9283200.

The previous prime is 21105169. The next prime is 21105179. The reversal of 21105172 is 27150112.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21105179) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6373 + ... + 9100.

It is an arithmetic number, because the mean of its divisors is an integer number (1733088).

Almost surely, 2^21105172 is an apocalyptic number.

21105172 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

21105172 is a deficient number, since it is larger than the sum of its proper divisors (20488940).

21105172 is a wasteful number, since it uses less digits than its factorization.

21105172 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15519 (or 15517 counting only the distinct ones).

The product of its (nonzero) digits is 140, while the sum is 19.

The square root of 21105172 is about 4594.0365692928. The cubic root of 21105172 is about 276.3522248158.

Adding to 21105172 its reverse (27150112), we get a palindrome (48255284).

The spelling of 21105172 in words is "twenty-one million, one hundred five thousand, one hundred seventy-two".