21645221 has 8 divisors (see below), whose sum is σ = 23659104. Its totient is φ = 19681200.

The previous prime is 21645203. The next prime is 21645229. The reversal of 21645221 is 12254612.

It is a happy number.

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 21645221 - 2¹⁰ = 21644197 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 (21645229) 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, 11555 + ... + 13296.

It is an arithmetic number, because the mean of its divisors is an integer number (2957388).

Almost surely, 2^21645221 is an apocalyptic number.

It is an amenable number.

21645221 is a deficient number, since it is larger than the sum of its proper divisors (2013883).

21645221 is a wasteful number, since it uses less digits than its factorization.

21645221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24931.

The product of its digits is 960, while the sum is 23.

The square root of 21645221 is about 4652.4424768072. The cubic root of 21645221 is about 278.6895438880.

Adding to 21645221 its reverse (12254612), we get a palindrome (33899833).

The spelling of 21645221 in words is "twenty-one million, six hundred forty-five thousand, two hundred twenty-one".