21144240 has 200 divisors, whose sum is σ = 79401168. Its totient is φ = 5184000.

The previous prime is 21144229. The next prime is 21144259. The reversal of 21144240 is 4244112.

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

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 84115 + ... + 84365.

Almost surely, 2^21144240 is an apocalyptic number.

21144240 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 21144240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39700584).

21144240 is an abundant number, since it is smaller than the sum of its proper divisors (58256928).

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

21144240 is a wasteful number, since it uses less digits than its factorization.

21144240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 289 (or 274 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 18.

The square root of 21144240 is about 4598.2866374336. The cubic root of 21144240 is about 276.5226391848.

Adding to 21144240 its reverse (4244112), we get a palindrome (25388352).

The spelling of 21144240 in words is "twenty-one million, one hundred forty-four thousand, two hundred forty".