21123312 has 80 divisors (see below), whose sum is σ = 63686400. Its totient is φ = 6030528.

The previous prime is 21123301. The next prime is 21123313. The reversal of 21123312 is 21332112.

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 21123291 and 21123300.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21123313) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 15823 + ... + 17105.

It is an arithmetic number, because the mean of its divisors is an integer number (796080).

Almost surely, 2^21123312 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 21123312, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31843200).

21123312 is an abundant number, since it is smaller than the sum of its proper divisors (42563088).

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

21123312 is a wasteful number, since it uses less digits than its factorization.

21123312 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1315 (or 1295 counting only the distinct ones).

The product of its digits is 72, while the sum is 15.

The square root of 21123312 is about 4596.0104438524. The cubic root of 21123312 is about 276.4313775120.

Adding to 21123312 its reverse (21332112), we get a palindrome (42455424).

The spelling of 21123312 in words is "twenty-one million, one hundred twenty-three thousand, three hundred twelve".