21209020 has 48 divisors (see below), whose sum is σ = 51226560. Its totient is φ = 7225344.

The previous prime is 21209017. The next prime is 21209021. The reversal of 21209020 is 2090212.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 21208985 and 21209003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21209021) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 27196 + ... + 27964.

It is an arithmetic number, because the mean of its divisors is an integer number (1067220).

Almost surely, 2^21209020 is an apocalyptic number.

21209020 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 21209020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25613280).

21209020 is an abundant number, since it is smaller than the sum of its proper divisors (30017540).

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

21209020 is a wasteful number, since it uses less digits than its factorization.

21209020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 982 (or 980 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 16.

The square root of 21209020 is about 4605.3251785297. The cubic root of 21209020 is about 276.8047471259.

Adding to 21209020 its reverse (2090212), we get a palindrome (23299232).

The spelling of 21209020 in words is "twenty-one million, two hundred nine thousand, twenty".