21696221 has 4 divisors (see below), whose sum is σ = 21765852. Its totient is φ = 21626592.

The previous prime is 21696217. The next prime is 21696277. The reversal of 21696221 is 12269612.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3463321 + 18232900 = 1861^2 + 4270^2 .

It is a cyclic number.

It is not a de Polignac number, because 21696221 - 2² = 21696217 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21696211) 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, 34346 + ... + 34971.

It is an arithmetic number, because the mean of its divisors is an integer number (5441463).

Almost surely, 2^21696221 is an apocalyptic number.

It is an amenable number.

21696221 is a deficient number, since it is larger than the sum of its proper divisors (69631).

21696221 is an equidigital number, since it uses as much as digits as its factorization.

21696221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 69630.

The product of its digits is 2592, while the sum is 29.

The square root of 21696221 is about 4657.9202440574. The cubic root of 21696221 is about 278.9082529571.

The spelling of 21696221 in words is "twenty-one million, six hundred ninety-six thousand, two hundred twenty-one".