21021221 has 8 divisors (see below), whose sum is σ = 22714104. Its totient is φ = 19339200.

The previous prime is 21021181. The next prime is 21021229. The reversal of 21021221 is 12212012.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 4120900 + 16900321 = 2030^2 + 4111^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21021221 - 2⁶ = 21021157 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021229) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1571 + ... + 6671.

It is an arithmetic number, because the mean of its divisors is an integer number (2839263).

Almost surely, 2^21021221 is an apocalyptic number.

It is an amenable number.

21021221 is a deficient number, since it is larger than the sum of its proper divisors (1692883).

21021221 is a wasteful number, since it uses less digits than its factorization.

21021221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5431.

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

The square root of 21021221 is about 4584.8905112336. The cubic root of 21021221 is about 275.9853183047.

Adding to 21021221 its reverse (12212012), we get a palindrome (33233233).

The spelling of 21021221 in words is "twenty-one million, twenty-one thousand, two hundred twenty-one".