21540840 has 64 divisors (see below), whose sum is σ = 65534400. Its totient is φ = 5663232.

The previous prime is 21540833. The next prime is 21540847. The reversal of 21540840 is 4804512.

It is an interprime number because it is at equal distance from previous prime (21540833) and next prime (21540847).

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 21540840.

It is not an unprimeable number, because it can be changed into a prime (21540847) by changing a digit.

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, 7531 + ... + 9989.

It is an arithmetic number, because the mean of its divisors is an integer number (1023975).

Almost surely, 2^21540840 is an apocalyptic number.

21540840 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 21540840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32767200).

21540840 is an abundant number, since it is smaller than the sum of its proper divisors (43993560).

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

21540840 is a wasteful number, since it uses less digits than its factorization.

21540840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2546 (or 2542 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 24.

The square root of 21540840 is about 4641.2110488535. The cubic root of 21540840 is about 278.2408416150.

The spelling of 21540840 in words is "twenty-one million, five hundred forty thousand, eight hundred forty".