21221021 has 2 divisors, whose sum is σ = 21221022. Its totient is φ = 21221020.

The previous prime is 21221003. The next prime is 21221033. The reversal of 21221021 is 12012212.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18705625 + 2515396 = 4325^2 + 1586^2 .

It is a cyclic number.

It is not a de Polignac number, because 21221021 - 2¹⁰ = 21219997 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21220993 and 21221011.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21221051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10610510 + 10610511.

It is an arithmetic number, because the mean of its divisors is an integer number (10610511).

Almost surely, 2^21221021 is an apocalyptic number.

It is an amenable number.

21221021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21221021 is an equidigital number, since it uses as much as digits as its factorization.

21221021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 16, while the sum is 11.

The square root of 21221021 is about 4606.6279424325. The cubic root of 21221021 is about 276.8569467309.

Adding to 21221021 its reverse (12012212), we get a palindrome (33233233).

The spelling of 21221021 in words is "twenty-one million, two hundred twenty-one thousand, twenty-one".