21123256 has 64 divisors (see below), whose sum is σ = 50388480. Its totient is φ = 8062080.

The previous prime is 21123211. The next prime is 21123287. The reversal of 21123256 is 65232112.

It is a Harshad number since it is a multiple of its sum of digits (22).

Its product of digits (720) is a multiple of the sum of its prime divisors (720).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 32325 + ... + 32971.

It is an arithmetic number, because the mean of its divisors is an integer number (787320).

Almost surely, 2^21123256 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21123256, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25194240).

21123256 is an abundant number, since it is smaller than the sum of its proper divisors (29265224).

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

21123256 is a wasteful number, since it uses less digits than its factorization.

21123256 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 724 (or 720 counting only the distinct ones).

The product of its digits is 720, while the sum is 22.

The square root of 21123256 is about 4596.0043516080. The cubic root of 21123256 is about 276.4311332294.

Adding to 21123256 its reverse (65232112), we get a palindrome (86355368).

The spelling of 21123256 in words is "twenty-one million, one hundred twenty-three thousand, two hundred fifty-six".