21531312 has 160 divisors (see below), whose sum is σ = 70709760. Its totient is φ = 6209280.

The previous prime is 21531269. The next prime is 21531317. The reversal of 21531312 is 21313512.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is not an unprimeable number, because it can be changed into a prime (21531317) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 109198 + ... + 109394.

It is an arithmetic number, because the mean of its divisors is an integer number (441936).

Almost surely, 2^21531312 is an apocalyptic number.

21531312 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21531312, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35354880).

21531312 is an abundant number, since it is smaller than the sum of its proper divisors (49178448).

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

21531312 is a wasteful number, since it uses less digits than its factorization.

21531312 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 248 (or 236 counting only the distinct ones).

The product of its digits is 180, while the sum is 18.

The square root of 21531312 is about 4640.1844790913. The cubic root of 21531312 is about 278.1998114956.

Adding to 21531312 its reverse (21313512), we get a palindrome (42844824).

The spelling of 21531312 in words is "twenty-one million, five hundred thirty-one thousand, three hundred twelve".