21881312 has 96 divisors (see below), whose sum is σ = 50349600. Its totient is φ = 9289728.

The previous prime is 21881297. The next prime is 21881351. The reversal of 21881312 is 21318812.

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, 299708 + ... + 299780.

It is an arithmetic number, because the mean of its divisors is an integer number (524475).

Almost surely, 2^21881312 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 21881312, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25174800).

21881312 is an abundant number, since it is smaller than the sum of its proper divisors (28468288).

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

21881312 is a wasteful number, since it uses less digits than its factorization.

21881312 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 148 (or 140 counting only the distinct ones).

The product of its digits is 768, while the sum is 26.

The square root of 21881312 is about 4677.7464659812. The cubic root of 21881312 is about 279.6991326082.

Subtracting from 21881312 its reverse (21318812), we obtain a square (562500 = 750²).

The spelling of 21881312 in words is "twenty-one million, eight hundred eighty-one thousand, three hundred twelve".