21228973 has 4 divisors (see below), whose sum is σ = 21251808. Its totient is φ = 21206140.

The previous prime is 21228953. The next prime is 21228979. The reversal of 21228973 is 37982212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21228973 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21228979) 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, 9961 + ... + 11902.

It is an arithmetic number, because the mean of its divisors is an integer number (5312952).

Almost surely, 2^21228973 is an apocalyptic number.

It is an amenable number.

21228973 is a deficient number, since it is larger than the sum of its proper divisors (22835).

21228973 is an equidigital number, since it uses as much as digits as its factorization.

21228973 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22834.

The product of its digits is 12096, while the sum is 34.

The square root of 21228973 is about 4607.4909658077. The cubic root of 21228973 is about 276.8915239473.

It can be divided in two parts, 21228 and 973, that added together give a square (22201 = 149²).

The spelling of 21228973 in words is "twenty-one million, two hundred twenty-eight thousand, nine hundred seventy-three".