21321220 has 24 divisors (see below), whose sum is σ = 44944704. Its totient is φ = 8496096.

The previous prime is 21321217. The next prime is 21321263. The reversal of 21321220 is 2212312.

It is a self number, because there is not a number n which added to its sum of digits gives 21321220.

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, 3777 + ... + 7543.

It is an arithmetic number, because the mean of its divisors is an integer number (1872696).

Almost surely, 2^21321220 is an apocalyptic number.

21321220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21321220 is an abundant number, since it is smaller than the sum of its proper divisors (23623484).

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

21321220 is a wasteful number, since it uses less digits than its factorization.

21321220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4059 (or 4057 counting only the distinct ones).

The product of its (nonzero) digits is 48, while the sum is 13.

The square root of 21321220 is about 4617.4906605211. The cubic root of 21321220 is about 277.2920065752.

Adding to 21321220 its reverse (2212312), we get a palindrome (23533532).

The spelling of 21321220 in words is "twenty-one million, three hundred twenty-one thousand, two hundred twenty".