21722761 has 4 divisors (see below), whose sum is σ = 21745300. Its totient is φ = 21700224.

The previous prime is 21722759. The next prime is 21722791. The reversal of 21722761 is 16722712.

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 5035536 + 16687225 = 2244^2 + 4085^2 .

It is a cyclic number.

It is not a de Polignac number, because 21722761 - 2¹ = 21722759 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21722791) 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 3 ways as a sum of consecutive naturals, for example, 9756 + ... + 11773.

It is an arithmetic number, because the mean of its divisors is an integer number (5436325).

Almost surely, 2^21722761 is an apocalyptic number.

It is an amenable number.

21722761 is a deficient number, since it is larger than the sum of its proper divisors (22539).

21722761 is a wasteful number, since it uses less digits than its factorization.

21722761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22538.

The product of its digits is 2352, while the sum is 28.

The square root of 21722761 is about 4660.7682843068. The cubic root of 21722761 is about 279.0219318756.

The spelling of 21722761 in words is "twenty-one million, seven hundred twenty-two thousand, seven hundred sixty-one".