21722561 has 16 divisors (see below), whose sum is σ = 25488000. Its totient is φ = 18129408.

The previous prime is 21722543. The next prime is 21722587. The reversal of 21722561 is 16522712.

It is a cyclic number.

It is not a de Polignac number, because 21722561 - 2¹⁴ = 21706177 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21722561.

It is not an unprimeable number, because it can be changed into a prime (21722531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 61361 + ... + 61713.

It is an arithmetic number, because the mean of its divisors is an integer number (1593000).

Almost surely, 2^21722561 is an apocalyptic number.

It is an amenable number.

21722561 is a deficient number, since it is larger than the sum of its proper divisors (3765439).

21722561 is a wasteful number, since it uses less digits than its factorization.

21722561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 568.

The product of its digits is 1680, while the sum is 26.

The square root of 21722561 is about 4660.7468285673. The cubic root of 21722561 is about 279.0210755609.

The spelling of 21722561 in words is "twenty-one million, seven hundred twenty-two thousand, five hundred sixty-one".