21530220 has 48 divisors (see below), whose sum is σ = 60546528. Its totient is φ = 5716480.

The previous prime is 21530161. The next prime is 21530227. The reversal of 21530220 is 2203512.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21530220.

It is not an unprimeable number, because it can be changed into a prime (21530227) 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, 16222 + ... + 17498.

It is an arithmetic number, because the mean of its divisors is an integer number (1261386).

Almost surely, 2^21530220 is an apocalyptic number.

21530220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21530220 is an abundant number, since it is smaller than the sum of its proper divisors (39016308).

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

21530220 is a wasteful number, since it uses less digits than its factorization.

21530220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1570 (or 1568 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 15.

The square root of 21530220 is about 4640.0668098638. The cubic root of 21530220 is about 278.1951082781.

Adding to 21530220 its reverse (2203512), we get a palindrome (23733732).

The spelling of 21530220 in words is "twenty-one million, five hundred thirty thousand, two hundred twenty".