21355221 has 8 divisors (see below), whose sum is σ = 29972320. Its totient is φ = 13487472.

The previous prime is 21355207. The next prime is 21355231. The reversal of 21355221 is 12255312.

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

It is not a de Polignac number, because 21355221 - 2¹⁰ = 21354197 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 (21355231) 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, 187270 + ... + 187383.

It is an arithmetic number, because the mean of its divisors is an integer number (3746540).

Almost surely, 2^21355221 is an apocalyptic number.

It is an amenable number.

21355221 is a deficient number, since it is larger than the sum of its proper divisors (8617099).

21355221 is a wasteful number, since it uses less digits than its factorization.

21355221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 374675.

The product of its digits is 600, while the sum is 21.

The square root of 21355221 is about 4621.1709555047. The cubic root of 21355221 is about 277.4393276982.

Subtracting from 21355221 its reverse (12255312), we obtain a palindrome (9099909).

The spelling of 21355221 in words is "twenty-one million, three hundred fifty-five thousand, two hundred twenty-one".