21224821 has 2 divisors, whose sum is σ = 21224822. Its totient is φ = 21224820.

The previous prime is 21224813. The next prime is 21224849. The reversal of 21224821 is 12842212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20520900 + 703921 = 4530^2 + 839^2 .

It is a cyclic number.

It is not a de Polignac number, because 21224821 - 2³ = 21224813 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21224792 and 21224801.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21224321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10612410 + 10612411.

It is an arithmetic number, because the mean of its divisors is an integer number (10612411).

Almost surely, 2^21224821 is an apocalyptic number.

It is an amenable number.

21224821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21224821 is an equidigital number, since it uses as much as digits as its factorization.

21224821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 512, while the sum is 22.

The square root of 21224821 is about 4607.0403731680. The cubic root of 21224821 is about 276.8734711260.

The spelling of 21224821 in words is "twenty-one million, two hundred twenty-four thousand, eight hundred twenty-one".