21242880 has 132 divisors (see below), whose sum is σ = 73765692. Its totient is φ = 5652480.

The previous prime is 21242873. The next prime is 21242917. The reversal of 21242880 is 8824212.

It is a Cunningham number, because it is equal to 4609²-1.

It can be written as a sum of positive squares in 2 ways, for example, as 7225344 + 14017536 = 2688^2 + 3744^2 .

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 45850 + ... + 46310.

It is an arithmetic number, because the mean of its divisors is an integer number (558831).

Almost surely, 2^21242880 is an apocalyptic number.

21242880 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 21242880, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36882846).

21242880 is an abundant number, since it is smaller than the sum of its proper divisors (52522812).

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

21242880 is a wasteful number, since it uses less digits than its factorization.

21242880 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 492 (or 471 counting only the distinct ones).

The product of its (nonzero) digits is 2048, while the sum is 27.

The square root of 21242880 is about 4608.9998915166. Note that the first 3 decimals coincide. The cubic root of 21242880 is about 276.9519741924.

It can be divided in two parts, 21242 and 880, that added together give a palindrome (22122).

The spelling of 21242880 in words is "twenty-one million, two hundred forty-two thousand, eight hundred eighty".