21928221 has 24 divisors (see below), whose sum is σ = 36489024. Its totient is φ = 12430080.

The previous prime is 21928217. The next prime is 21928241. The reversal of 21928221 is 12282912.

It is not a de Polignac number, because 21928221 - 2² = 21928217 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21928241) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6925 + ... + 9581.

It is an arithmetic number, because the mean of its divisors is an integer number (1520376).

Almost surely, 2^21928221 is an apocalyptic number.

21928221 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21928221 is a deficient number, since it is larger than the sum of its proper divisors (14560803).

21928221 is a wasteful number, since it uses less digits than its factorization.

21928221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2801 (or 2798 counting only the distinct ones).

The product of its digits is 1152, while the sum is 27.

The square root of 21928221 is about 4682.7578412726. The cubic root of 21928221 is about 279.8988622824.

The spelling of 21928221 in words is "twenty-one million, nine hundred twenty-eight thousand, two hundred twenty-one".