21624240 has 80 divisors (see below), whose sum is σ = 73138176. Its totient is φ = 5241600.

The previous prime is 21624203. The next prime is 21624263. The reversal of 21624240 is 4242612.

It is a tau number, because it is divible by the number of its divisors (80).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1456 + ... + 6735.

Almost surely, 2^21624240 is an apocalyptic number.

21624240 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 21624240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36569088).

21624240 is an abundant number, since it is smaller than the sum of its proper divisors (51513936).

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

21624240 is a wasteful number, since it uses less digits than its factorization.

21624240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8218 (or 8212 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 21.

The square root of 21624240 is about 4650.1870930103. The cubic root of 21624240 is about 278.5994689535.

Adding to 21624240 its reverse (4242612), we get a palindrome (25866852).

The spelling of 21624240 in words is "twenty-one million, six hundred twenty-four thousand, two hundred forty".