21009220 has 24 divisors (see below), whose sum is σ = 45197208. Its totient is φ = 8198400.

The previous prime is 21009217. The next prime is 21009271. The reversal of 21009220 is 2290012.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 379456 + 20629764 = 616^2 + 4542^2 .

It is a plaindrome in base 13.

It is a junction number, because it is equal to n+sod(n) for n = 21009194 and 21009203.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11991 + ... + 13630.

It is an arithmetic number, because the mean of its divisors is an integer number (1883217).

Almost surely, 2^21009220 is an apocalyptic number.

21009220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21009220 is an abundant number, since it is smaller than the sum of its proper divisors (24187988).

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

21009220 is a wasteful number, since it uses less digits than its factorization.

21009220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25671 (or 25669 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 16.

The square root of 21009220 is about 4583.5815690353. The cubic root of 21009220 is about 275.9327883668.

Adding to 21009220 its reverse (2290012), we get a palindrome (23299232).

The spelling of 21009220 in words is "twenty-one million, nine thousand, two hundred twenty".