21123755 has 8 divisors (see below), whose sum is σ = 25595232. Its totient is φ = 16734528.

The previous prime is 21123721. The next prime is 21123757. The reversal of 21123755 is 55732112.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21123755 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21123757) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 19994 + ... + 21023.

It is an arithmetic number, because the mean of its divisors is an integer number (3199404).

Almost surely, 2^21123755 is an apocalyptic number.

21123755 is a deficient number, since it is larger than the sum of its proper divisors (4471477).

21123755 is a wasteful number, since it uses less digits than its factorization.

21123755 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41125.

The product of its digits is 2100, while the sum is 26.

The square root of 21123755 is about 4596.0586375720. The cubic root of 21123755 is about 276.4333099464.

Adding to 21123755 its reverse (55732112), we get a palindrome (76855867).

The spelling of 21123755 in words is "twenty-one million, one hundred twenty-three thousand, seven hundred fifty-five".