21123821 has 8 divisors (see below), whose sum is σ = 22512384. Its totient is φ = 19774480.

The previous prime is 21123779. The next prime is 21123841. The reversal of 21123821 is 12832112.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21123821 - 2⁶ = 21123757 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21123793 and 21123802.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21123841) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8690 + ... + 10851.

It is an arithmetic number, because the mean of its divisors is an integer number (2814048).

Almost surely, 2^21123821 is an apocalyptic number.

It is an amenable number.

21123821 is a deficient number, since it is larger than the sum of its proper divisors (1388563).

21123821 is a wasteful number, since it uses less digits than its factorization.

21123821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19611.

The product of its digits is 192, while the sum is 20.

The square root of 21123821 is about 4596.0658176314. The cubic root of 21123821 is about 276.4335978463.

Adding to 21123821 its reverse (12832112), we get a palindrome (33955933).

The spelling of 21123821 in words is "twenty-one million, one hundred twenty-three thousand, eight hundred twenty-one".