21209244 has 96 divisors (see below), whose sum is σ = 60587520. Its totient is φ = 5640192.

The previous prime is 21209231. The next prime is 21209311. The reversal of 21209244 is 44290212.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 154744 + ... + 154880.

It is an arithmetic number, because the mean of its divisors is an integer number (631120).

Almost surely, 2^21209244 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 21209244, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30293760).

21209244 is an abundant number, since it is smaller than the sum of its proper divisors (39378276).

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

21209244 is a wasteful number, since it uses less digits than its factorization.

21209244 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 267 (or 265 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 24.

The square root of 21209244 is about 4605.3494981380. The cubic root of 21209244 is about 276.8057216176.

Adding to 21209244 its reverse (44290212), we get a palindrome (65499456).

The spelling of 21209244 in words is "twenty-one million, two hundred nine thousand, two hundred forty-four".