21201220 has 12 divisors (see below), whose sum is σ = 44522604. Its totient is φ = 8480480.

The previous prime is 21201209. The next prime is 21201251. The reversal of 21201220 is 2210212.

It can be written as a sum of positive squares in 2 ways, for example, as 5008644 + 16192576 = 2238^2 + 4024^2 .

It is a Harshad number since it is a multiple of its sum of digits (10).

It is a junction number, because it is equal to n+sod(n) for n = 21201197 and 21201206.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 530011 + ... + 530050.

It is an arithmetic number, because the mean of its divisors is an integer number (3710217).

Almost surely, 2^21201220 is an apocalyptic number.

21201220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21201220 is an abundant number, since it is smaller than the sum of its proper divisors (23321384).

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

21201220 is a wasteful number, since it uses less digits than its factorization.

21201220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1060070 (or 1060068 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 10.

The square root of 21201220 is about 4604.4782549166. The cubic root of 21201220 is about 276.7708096508.

Adding to 21201220 its reverse (2210212), we get a palindrome (23411432).

The spelling of 21201220 in words is "twenty-one million, two hundred one thousand, two hundred twenty".