21027840 has 132 divisors (see below), whose sum is σ = 69123096. Its totient is φ = 5455872.

The previous prime is 21027833. The next prime is 21027841. The reversal of 21027840 is 4872012.

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 21027840.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21027841) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 568302 + ... + 568338.

Almost surely, 2^21027840 is an apocalyptic number.

21027840 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 21027840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34561548).

21027840 is an abundant number, since it is smaller than the sum of its proper divisors (48095256).

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

21027840 is an equidigital number, since it uses as much as digits as its factorization.

21027840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 102 (or 47 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 24.

The square root of 21027840 is about 4585.6122819096. The cubic root of 21027840 is about 276.0142819747.

Adding to 21027840 its reverse (4872012), we get a palindrome (25899852).

The spelling of 21027840 in words is "twenty-one million, twenty-seven thousand, eight hundred forty".