21855761 has 4 divisors (see below), whose sum is σ = 23141412. Its totient is φ = 20570112.

The previous prime is 21855737. The next prime is 21855781. The reversal of 21855761 is 16755812.

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 14326225 + 7529536 = 3785^2 + 2744^2 .

It is a cyclic number.

It is not a de Polignac number, because 21855761 - 2⁶ = 21855697 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21855781) 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, 642800 + ... + 642833.

It is an arithmetic number, because the mean of its divisors is an integer number (5785353).

Almost surely, 2^21855761 is an apocalyptic number.

It is an amenable number.

21855761 is a deficient number, since it is larger than the sum of its proper divisors (1285651).

21855761 is a wasteful number, since it uses less digits than its factorization.

21855761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1285650.

The product of its digits is 16800, while the sum is 35.

The square root of 21855761 is about 4675.0145454319. The cubic root of 21855761 is about 279.5902211612.

The spelling of 21855761 in words is "twenty-one million, eight hundred fifty-five thousand, seven hundred sixty-one".