21215520 has 120 divisors (see below), whose sum is σ = 74918844. Its totient is φ = 5654016.

The previous prime is 21215503. The next prime is 21215539. The reversal of 21215520 is 2551212.

It can be written as a sum of positive squares in 2 ways, for example, as 18352656 + 2862864 = 4284^2 + 1692^2 .

It is a tau number, because it is divible by the number of its divisors (120).

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

It is a junction number, because it is equal to n+sod(n) for n = 21215493 and 21215502.

It is an unprimeable number.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 12142 + ... + 13778.

Almost surely, 2^21215520 is an apocalyptic number.

21215520 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 21215520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37459422).

21215520 is an abundant number, since it is smaller than the sum of its proper divisors (53703324).

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

21215520 is a wasteful number, since it uses less digits than its factorization.

21215520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1664 (or 1647 counting only the distinct ones).

The product of its (nonzero) digits is 200, while the sum is 18.

The square root of 21215520 is about 4606.0308292498. The cubic root of 21215520 is about 276.8330219995.

Adding to 21215520 its reverse (2551212), we get a palindrome (23766732).

The spelling of 21215520 in words is "twenty-one million, two hundred fifteen thousand, five hundred twenty".