21223755 has 64 divisors (see below), whose sum is σ = 44359680. Its totient is φ = 9424512.

The previous prime is 21223739. The next prime is 21223757. The reversal of 21223755 is 55732212.

It is not a de Polignac number, because 21223755 - 2⁴ = 21223739 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21223757) 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 63 ways as a sum of consecutive naturals, for example, 34662 + ... + 35268.

It is an arithmetic number, because the mean of its divisors is an integer number (693120).

Almost surely, 2^21223755 is an apocalyptic number.

21223755 is an abundant number, since it is smaller than the sum of its proper divisors (23135925).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21223755 is a wasteful number, since it uses less digits than its factorization.

21223755 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 665 (or 659 counting only the distinct ones).

The product of its digits is 4200, while the sum is 27.

The square root of 21223755 is about 4606.9246792193. The cubic root of 21223755 is about 276.8688357974.

Adding to 21223755 its reverse (55732212), we get a palindrome (76955967).

The spelling of 21223755 in words is "twenty-one million, two hundred twenty-three thousand, seven hundred fifty-five".