21815040 has 288 divisors, whose sum is σ = 82414080. Its totient is φ = 4866048.

The previous prime is 21815039. The next prime is 21815051. The reversal of 21815040 is 4051812.

It is a junction number, because it is equal to n+sod(n) for n = 21814998 and 21815016.

It is a congruent number.

It is an unprimeable number.

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 31 ways as a sum of consecutive naturals, for example, 948469 + ... + 948491.

It is an arithmetic number, because the mean of its divisors is an integer number (286160).

Almost surely, 2^21815040 is an apocalyptic number.

21815040 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 21815040, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (41207040).

21815040 is an abundant number, since it is smaller than the sum of its proper divisors (60599040).

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

21815040 is a wasteful number, since it uses less digits than its factorization.

21815040 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 79 (or 65 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 21.

The square root of 21815040 is about 4670.6573413172. The cubic root of 21815040 is about 279.4164718299.

Adding to 21815040 its reverse (4051812), we get a palindrome (25866852).

The spelling of 21815040 in words is "twenty-one million, eight hundred fifteen thousand, forty".