21618240 has 112 divisors (see below), whose sum is σ = 78467712. Its totient is φ = 4939776.

The previous prime is 21618227. The next prime is 21618241. The reversal of 21618240 is 4281612.

It is a tau number, because it is divible by the number of its divisors (112).

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21618240.

It is not an unprimeable number, because it can be changed into a prime (21618241) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 5112 + ... + 8328.

Almost surely, 2^21618240 is an apocalyptic number.

21618240 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 21618240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39233856).

21618240 is an abundant number, since it is smaller than the sum of its proper divisors (56849472).

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

21618240 is a wasteful number, since it uses less digits than its factorization.

21618240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3244 (or 3234 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 24.

The square root of 21618240 is about 4649.5419129200. The cubic root of 21618240 is about 278.5736992395.

Adding to 21618240 its reverse (4281612), we get a palindrome (25899852).

It can be divided in two parts, 2161 and 8240, that added together give a palindrome (10401).

The spelling of 21618240 in words is "twenty-one million, six hundred eighteen thousand, two hundred forty".