21020221 has 4 divisors (see below), whose sum is σ = 21228444. Its totient is φ = 20812000.

The previous prime is 21020161. The next prime is 21020227. The reversal of 21020221 is 12202012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11323225 + 9696996 = 3365^2 + 3114^2 .

It is a cyclic number.

It is not a de Polignac number, because 21020221 - 2⁷ = 21020093 is a prime.

It is a super-3 number, since 3×21020221³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21020198 and 21020207.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21020227) 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 in 3 ways as a sum of consecutive naturals, for example, 103960 + ... + 104161.

It is an arithmetic number, because the mean of its divisors is an integer number (5307111).

Almost surely, 2^21020221 is an apocalyptic number.

It is an amenable number.

21020221 is a deficient number, since it is larger than the sum of its proper divisors (208223).

21020221 is a wasteful number, since it uses less digits than its factorization.

21020221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 208222.

The product of its (nonzero) digits is 16, while the sum is 10.

The square root of 21020221 is about 4584.7814560784. The cubic root of 21020221 is about 275.9809419383.

Adding to 21020221 its reverse (12202012), we get a palindrome (33222233).

The spelling of 21020221 in words is "twenty-one million, twenty thousand, two hundred twenty-one".