21003821 has 2 divisors, whose sum is σ = 21003822. Its totient is φ = 21003820.

The previous prime is 21003811. The next prime is 21003869. The reversal of 21003821 is 12830012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17724100 + 3279721 = 4210^2 + 1811^2 .

It is a cyclic number.

It is not a de Polignac number, because 21003821 - 2¹⁰ = 21002797 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21003821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21003811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10501910 + 10501911.

It is an arithmetic number, because the mean of its divisors is an integer number (10501911).

Almost surely, 2^21003821 is an apocalyptic number.

It is an amenable number.

21003821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21003821 is an equidigital number, since it uses as much as digits as its factorization.

21003821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 96, while the sum is 17.

The square root of 21003821 is about 4582.9925812726. The cubic root of 21003821 is about 275.9091497174.

Adding to 21003821 its reverse (12830012), we get a palindrome (33833833).

The spelling of 21003821 in words is "twenty-one million, three thousand, eight hundred twenty-one".