21722161 has 4 divisors (see below), whose sum is σ = 22078324. Its totient is φ = 21366000.

The previous prime is 21722153. The next prime is 21722167. The reversal of 21722161 is 16122712.

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 846400 + 20875761 = 920^2 + 4569^2 .

It is a cyclic number.

It is not a de Polignac number, because 21722161 - 2³ = 21722153 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21722167) 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, 177990 + ... + 178111.

It is an arithmetic number, because the mean of its divisors is an integer number (5519581).

Almost surely, 2^21722161 is an apocalyptic number.

It is an amenable number.

21722161 is a deficient number, since it is larger than the sum of its proper divisors (356163).

21722161 is an equidigital number, since it uses as much as digits as its factorization.

21722161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 356162.

The product of its digits is 336, while the sum is 22.

The square root of 21722161 is about 4660.7039167920. The cubic root of 21722161 is about 279.0193629158.

Adding to 21722161 its reverse (16122712), we get a palindrome (37844873).

The spelling of 21722161 in words is "twenty-one million, seven hundred twenty-two thousand, one hundred sixty-one".