21071221 has 2 divisors, whose sum is σ = 21071222. Its totient is φ = 21071220.

The previous prime is 21071203. The next prime is 21071249. The reversal of 21071221 is 12217012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17514225 + 3556996 = 4185^2 + 1886^2 .

It is a cyclic number.

It is not a de Polignac number, because 21071221 - 2¹⁷ = 20940149 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21071195 and 21071204.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21071251) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10535610 + 10535611.

It is an arithmetic number, because the mean of its divisors is an integer number (10535611).

Almost surely, 2^21071221 is an apocalyptic number.

It is an amenable number.

21071221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21071221 is an equidigital number, since it uses as much as digits as its factorization.

21071221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 56, while the sum is 16.

The square root of 21071221 is about 4590.3399656235. The cubic root of 21071221 is about 276.2039598956.

Adding to 21071221 its reverse (12217012), we get a palindrome (33288233).

The spelling of 21071221 in words is "twenty-one million, seventy-one thousand, two hundred twenty-one".