21540820 has 48 divisors (see below), whose sum is σ = 51988608. Its totient is φ = 7344000.

The previous prime is 21540817. The next prime is 21540833. The reversal of 21540820 is 2804512.

It is a junction number, because it is equal to n+sod(n) for n = 21540791 and 21540800.

It is a congruent number.

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, 34834 + ... + 35446.

It is an arithmetic number, because the mean of its divisors is an integer number (1083096).

Almost surely, 2^21540820 is an apocalyptic number.

21540820 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 21540820, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25994304).

21540820 is an abundant number, since it is smaller than the sum of its proper divisors (30447788).

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

21540820 is a wasteful number, since it uses less digits than its factorization.

21540820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 880 (or 878 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 22.

The square root of 21540820 is about 4641.2088942430. The cubic root of 21540820 is about 278.2407555023.

The spelling of 21540820 in words is "twenty-one million, five hundred forty thousand, eight hundred twenty".