21221220 has 24 divisors (see below), whose sum is σ = 59419584. Its totient is φ = 5658976.

The previous prime is 21221171. The next prime is 21221237. The reversal of 21221220 is 2212212.

It is a Harshad number since it is a multiple of its sum of digits (12).

It is a junction number, because it is equal to n+sod(n) for n = 21221196 and 21221205.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 176784 + ... + 176903.

It is an arithmetic number, because the mean of its divisors is an integer number (2475816).

Almost surely, 2^21221220 is an apocalyptic number.

21221220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21221220 is an abundant number, since it is smaller than the sum of its proper divisors (38198364).

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

21221220 is a wasteful number, since it uses less digits than its factorization.

21221220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 353699 (or 353697 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 12.

The square root of 21221220 is about 4606.6495416951. The cubic root of 21221220 is about 276.8578121363.

Adding to 21221220 its reverse (2212212), we get a palindrome (23433432).

The spelling of 21221220 in words is "twenty-one million, two hundred twenty-one thousand, two hundred twenty".