21171921 has 16 divisors (see below), whose sum is σ = 28819200. Its totient is φ = 13822848.

The previous prime is 21171911. The next prime is 21171929. The reversal of 21171921 is 12917112.

It is not a de Polignac number, because 21171921 - 2¹¹ = 21169873 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21171891 and 21171900.

It is not an unprimeable number, because it can be changed into a prime (21171929) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 36925 + ... + 37493.

It is an arithmetic number, because the mean of its divisors is an integer number (1801200).

Almost surely, 2^21171921 is an apocalyptic number.

It is an amenable number.

21171921 is a deficient number, since it is larger than the sum of its proper divisors (7647279).

21171921 is a wasteful number, since it uses less digits than its factorization.

21171921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 808.

The product of its digits is 252, while the sum is 24.

The square root of 21171921 is about 4601.2955784214. The cubic root of 21171921 is about 276.6432565150.

The spelling of 21171921 in words is "twenty-one million, one hundred seventy-one thousand, nine hundred twenty-one".