21225204 has 288 divisors, whose sum is σ = 78274560. Its totient is φ = 4665600.

The previous prime is 21225203. The next prime is 21225209. The reversal of 21225204 is 40252212.

Added to its reverse (40252212) it gives a triangular number (61477416 = T₁₁₀₈₈).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21225203) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 684669 + ... + 684699.

Almost surely, 2^21225204 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21225204, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39137280).

21225204 is an abundant number, since it is smaller than the sum of its proper divisors (57049356).

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

21225204 is a wasteful number, since it uses less digits than its factorization.

21225204 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91 (or 86 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 18.

The square root of 21225204 is about 4607.0819397966. The cubic root of 21225204 is about 276.8751365017.

Adding to 21225204 its reverse (40252212), we get a palindrome (61477416).

The spelling of 21225204 in words is "twenty-one million, two hundred twenty-five thousand, two hundred four".