21722181 has 16 divisors (see below), whose sum is σ = 31918656. Its totient is φ = 13055616.

The previous prime is 21722167. The next prime is 21722201. The reversal of 21722181 is 18122712.

It is not a de Polignac number, because 21722181 - 2⁶ = 21722117 is a prime.

It is a super-2 number, since 2×21722181² = 943706294793522, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21722101) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4800 + ... + 8153.

It is an arithmetic number, because the mean of its divisors is an integer number (1994916).

Almost surely, 2^21722181 is an apocalyptic number.

It is an amenable number.

21722181 is a deficient number, since it is larger than the sum of its proper divisors (10196475).

21722181 is a wasteful number, since it uses less digits than its factorization.

21722181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13012.

The product of its digits is 448, while the sum is 24.

The square root of 21722181 is about 4660.7060623901. The cubic root of 21722181 is about 279.0194485485.

Adding to 21722181 its reverse (18122712), we get a palindrome (39844893).

The spelling of 21722181 in words is "twenty-one million, seven hundred twenty-two thousand, one hundred eighty-one".