21636221 has 4 divisors (see below), whose sum is σ = 21718752. Its totient is φ = 21553692.

The previous prime is 21636217. The next prime is 21636227. The reversal of 21636221 is 12263612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21636221 - 2² = 21636217 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 (21636227) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 40871 + ... + 41396.

It is an arithmetic number, because the mean of its divisors is an integer number (5429688).

Almost surely, 2^21636221 is an apocalyptic number.

It is an amenable number.

21636221 is a deficient number, since it is larger than the sum of its proper divisors (82531).

21636221 is an equidigital number, since it uses as much as digits as its factorization.

21636221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 82530.

The product of its digits is 864, while the sum is 23.

The square root of 21636221 is about 4651.4751423608. The cubic root of 21636221 is about 278.6509125182.

Adding to 21636221 its reverse (12263612), we get a palindrome (33899833).

The spelling of 21636221 in words is "twenty-one million, six hundred thirty-six thousand, two hundred twenty-one".