21010221 has 12 divisors (see below), whose sum is σ = 30503200. Its totient is φ = 13935240.

The previous prime is 21010217. The next prime is 21010229. The reversal of 21010221 is 12201012.

It is not a de Polignac number, because 21010221 - 2² = 21010217 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21010229) 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 in 11 ways as a sum of consecutive naturals, for example, 4075 + ... + 7656.

Almost surely, 2^21010221 is an apocalyptic number.

It is an amenable number.

21010221 is a deficient number, since it is larger than the sum of its proper divisors (9492979).

21010221 is a wasteful number, since it uses less digits than its factorization.

21010221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11936 (or 11933 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 9.

The square root of 21010221 is about 4583.6907618207. The cubic root of 21010221 is about 275.9371706386.

Adding to 21010221 its reverse (12201012), we get a palindrome (33211233).

The spelling of 21010221 in words is "twenty-one million, ten thousand, two hundred twenty-one".