21531212440 has 64 divisors (see below), whose sum is σ = 50060448000. Its totient is φ = 8325918720.

The previous prime is 21531212413. The next prime is 21531212449. The reversal of 21531212440 is 4421213512.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531212449) 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, 1242556 + ... + 1259764.

It is an arithmetic number, because the mean of its divisors is an integer number (782194500).

Almost surely, 2^21531212440 is an apocalyptic number.

21531212440 is a gapful number since it is divisible by the number (20) 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 21531212440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25030224000).

21531212440 is an abundant number, since it is smaller than the sum of its proper divisors (28529235560).

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

21531212440 is a wasteful number, since it uses less digits than its factorization.

21531212440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18260 (or 18256 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 25.

Adding to 21531212440 its reverse (4421213512), we get a palindrome (25952425952).

The spelling of 21531212440 in words is "twenty-one billion, five hundred thirty-one million, two hundred twelve thousand, four hundred forty".