21299221 has 2 divisors, whose sum is σ = 21299222. Its totient is φ = 21299220.

The previous prime is 21299167. The next prime is 21299231. The reversal of 21299221 is 12299212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12215025 + 9084196 = 3495^2 + 3014^2 .

It is a cyclic number.

It is not a de Polignac number, because 21299221 - 2⁷ = 21299093 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21299221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21299231) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10649610 + 10649611.

It is an arithmetic number, because the mean of its divisors is an integer number (10649611).

Almost surely, 2^21299221 is an apocalyptic number.

It is an amenable number.

21299221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21299221 is an equidigital number, since it uses as much as digits as its factorization.

21299221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1296, while the sum is 28.

The square root of 21299221 is about 4615.1079077309. The cubic root of 21299221 is about 277.1966048099.

Subtracting from 21299221 its reverse (12299212), we obtain a palindrome (9000009).

The spelling of 21299221 in words is "twenty-one million, two hundred ninety-nine thousand, two hundred twenty-one".