21755823 has 4 divisors (see below), whose sum is σ = 29007768. Its totient is φ = 14503880.

The previous prime is 21755819. The next prime is 21755843. The reversal of 21755823 is 32855712.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21755823 - 2² = 21755819 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21755803) 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, 3625968 + ... + 3625973.

It is an arithmetic number, because the mean of its divisors is an integer number (7251942).

Almost surely, 2^21755823 is an apocalyptic number.

21755823 is a deficient number, since it is larger than the sum of its proper divisors (7251945).

21755823 is an equidigital number, since it uses as much as digits as its factorization.

21755823 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7251944.

The product of its digits is 16800, while the sum is 33.

The square root of 21755823 is about 4664.3137758946. The cubic root of 21755823 is about 279.1634170657.

It can be divided in two parts, 21755 and 823, that added together give a triangular number (22578 = T₂₁₂).

The spelling of 21755823 in words is "twenty-one million, seven hundred fifty-five thousand, eight hundred twenty-three".