21210020 has 72 divisors (see below), whose sum is σ = 50190504. Its totient is φ = 7483392.

The previous prime is 21210011. The next prime is 21210037. The reversal of 21210020 is 2001212.

It can be written as a sum of positive squares in 12 ways, for example, as 7974976 + 13235044 = 2824^2 + 3638^2 .

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 218612 + ... + 218708.

Almost surely, 2^21210020 is an apocalyptic number.

21210020 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 21210020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25095252).

21210020 is an abundant number, since it is smaller than the sum of its proper divisors (28980484).

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

21210020 is a wasteful number, since it uses less digits than its factorization.

21210020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 177 (or 146 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 8.

The square root of 21210020 is about 4605.4337472164. The cubic root of 21210020 is about 276.8090974824.

Adding to 21210020 its reverse (2001212), we get a palindrome (23211232).

The spelling of 21210020 in words is "twenty-one million, two hundred ten thousand, twenty".