21755623 has 4 divisors (see below), whose sum is σ = 21838608. Its totient is φ = 21672640.

The previous prime is 21755611. The next prime is 21755633. The reversal of 21755623 is 32655712.

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 21755623 - 2¹³ = 21747431 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21755633) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 41098 + ... + 41623.

It is an arithmetic number, because the mean of its divisors is an integer number (5459652).

Almost surely, 2^21755623 is an apocalyptic number.

21755623 is a deficient number, since it is larger than the sum of its proper divisors (82985).

21755623 is an equidigital number, since it uses as much as digits as its factorization.

21755623 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 82984.

The product of its digits is 12600, while the sum is 31.

The square root of 21755623 is about 4664.2923364643. The cubic root of 21755623 is about 279.1625616188.

It can be divided in two parts, 2 and 1755623, that added together give a square (1755625 = 1325²).

The spelling of 21755623 in words is "twenty-one million, seven hundred fifty-five thousand, six hundred twenty-three".