21084221 has 4 divisors (see below), whose sum is σ = 21093600. Its totient is φ = 21074844.

The previous prime is 21084187. The next prime is 21084227. The reversal of 21084221 is 12248012.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21084221 - 2¹⁰ = 21083197 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21084193 and 21084202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21084227) 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, 920 + ... + 6558.

It is an arithmetic number, because the mean of its divisors is an integer number (5273400).

Almost surely, 2^21084221 is an apocalyptic number.

It is an amenable number.

21084221 is a deficient number, since it is larger than the sum of its proper divisors (9379).

21084221 is an equidigital number, since it uses as much as digits as its factorization.

21084221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9378.

The product of its (nonzero) digits is 256, while the sum is 20.

The square root of 21084221 is about 4591.7557644108. The cubic root of 21084221 is about 276.2607500441.

It can be divided in two parts, 21084 and 221, that multiplied together give a palindrome (4659564).

The spelling of 21084221 in words is "twenty-one million, eighty-four thousand, two hundred twenty-one".