21111840 has 168 divisors, whose sum is σ = 75194028. Its totient is φ = 5598720.

The previous prime is 21111833. The next prime is 21111851. The reversal of 21111840 is 4811112.

It can be written as a sum of positive squares in 2 ways, for example, as 17740944 + 3370896 = 4212^2 + 1836^2 .

It is a Harshad number since it is a multiple of its sum of digits (18).

It is an unprimeable number.

It is a polite number, since it can be written in 27 ways as a sum of consecutive naturals, for example, 116550 + ... + 116730.

Almost surely, 2^21111840 is an apocalyptic number.

21111840 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 21111840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37597014).

21111840 is an abundant number, since it is smaller than the sum of its proper divisors (54082188).

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

21111840 is an equidigital number, since it uses as much as digits as its factorization.

21111840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 214 (or 191 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 18.

The square root of 21111840 is about 4594.7622354155. The cubic root of 21111840 is about 276.3813254648.

Adding to 21111840 its reverse (4811112), we get a palindrome (25922952).

The spelling of 21111840 in words is "twenty-one million, one hundred eleven thousand, eight hundred forty".