21642221 has 4 divisors (see below), whose sum is σ = 21674592. Its totient is φ = 21609852.

The previous prime is 21642217. The next prime is 21642233. The reversal of 21642221 is 12224612.

It is a happy number.

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 21642221 - 2² = 21642217 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21642193 and 21642202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21642281) 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, 15161 + ... + 16526.

It is an arithmetic number, because the mean of its divisors is an integer number (5418648).

Almost surely, 2^21642221 is an apocalyptic number.

It is an amenable number.

21642221 is a deficient number, since it is larger than the sum of its proper divisors (32371).

21642221 is an equidigital number, since it uses as much as digits as its factorization.

21642221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32370.

The product of its digits is 384, while the sum is 20.

The square root of 21642221 is about 4652.1200543408. The cubic root of 21642221 is about 278.6766679548.

Adding to 21642221 its reverse (12224612), we get a palindrome (33866833).

The spelling of 21642221 in words is "twenty-one million, six hundred forty-two thousand, two hundred twenty-one".