21181924 has 12 divisors (see below), whose sum is σ = 37170364. Its totient is φ = 10561824.

The previous prime is 21181907. The next prime is 21181933. The reversal of 21181924 is 42918112.

It can be written as a sum of positive squares in 2 ways, for example, as 17640000 + 3541924 = 4200^2 + 1882^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21181892 and 21181901.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5607 + ... + 8590.

Almost surely, 2^21181924 is an apocalyptic number.

It is an amenable number.

21181924 is a deficient number, since it is larger than the sum of its proper divisors (15988440).

21181924 is a wasteful number, since it uses less digits than its factorization.

21181924 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14574 (or 14572 counting only the distinct ones).

The product of its digits is 1152, while the sum is 28.

The square root of 21181924 is about 4602.3824265265. The cubic root of 21181924 is about 276.6868177771.

The spelling of 21181924 in words is "twenty-one million, one hundred eighty-one thousand, nine hundred twenty-four".