21002220 has 192 divisors, whose sum is σ = 72576000. Its totient is φ = 5018112.

The previous prime is 21002213. The next prime is 21002231. The reversal of 21002220 is 2220012.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a congruent number.

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 63 ways as a sum of consecutive naturals, for example, 235936 + ... + 236024.

It is an arithmetic number, because the mean of its divisors is an integer number (378000).

Almost surely, 2^21002220 is an apocalyptic number.

21002220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21002220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36288000).

21002220 is an abundant number, since it is smaller than the sum of its proper divisors (51573780).

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

21002220 is a wasteful number, since it uses less digits than its factorization.

21002220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 149 (or 141 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 9.

The square root of 21002220 is about 4582.8179104128. The cubic root of 21002220 is about 275.9021392188.

Adding to 21002220 its reverse (2220012), we get a palindrome (23222232).

The spelling of 21002220 in words is "twenty-one million, two thousand, two hundred twenty".