21099821 has 2 divisors, whose sum is σ = 21099822. Its totient is φ = 21099820.

The previous prime is 21099817. The next prime is 21099829. The reversal of 21099821 is 12899012.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19802500 + 1297321 = 4450^2 + 1139^2 .

It is a cyclic number.

It is not a de Polignac number, because 21099821 - 2² = 21099817 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21099829) 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 as a sum of consecutive naturals, namely, 10549910 + 10549911.

It is an arithmetic number, because the mean of its divisors is an integer number (10549911).

Almost surely, 2^21099821 is an apocalyptic number.

It is an amenable number.

21099821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21099821 is an equidigital number, since it uses as much as digits as its factorization.

21099821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2592, while the sum is 32.

The square root of 21099821 is about 4593.4541469356. The cubic root of 21099821 is about 276.3288674171.

The spelling of 21099821 in words is "twenty-one million, ninety-nine thousand, eight hundred twenty-one".