21215015520 has 96 divisors (see below), whose sum is σ = 66887003232. Its totient is φ = 5652283392.

The previous prime is 21215015519. The next prime is 21215015527. The reversal of 21215015520 is 2551051212.

It is a tau number, because it is divible by the number of its divisors (96).

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21215015527) 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, 534274 + ... + 572606.

It is an arithmetic number, because the mean of its divisors is an integer number (696739617).

Almost surely, 2^21215015520 is an apocalyptic number.

21215015520 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 21215015520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33443501616).

21215015520 is an abundant number, since it is smaller than the sum of its proper divisors (45671987712).

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

21215015520 is a wasteful number, since it uses less digits than its factorization.

21215015520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39504 (or 39496 counting only the distinct ones).

The product of its (nonzero) digits is 1000, while the sum is 24.

Adding to 21215015520 its reverse (2551051212), we get a palindrome (23766066732).

The spelling of 21215015520 in words is "twenty-one billion, two hundred fifteen million, fifteen thousand, five hundred twenty".