21818240 has 64 divisors (see below), whose sum is σ = 52986960. Its totient is φ = 8589312.

The previous prime is 21818227. The next prime is 21818267. The reversal of 21818240 is 4281812.

It is a Cunningham number, because it is equal to 4671²-1.

It is a tau number, because it is divible by the number of its divisors (64).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 46487 + ... + 46953.

Almost surely, 2^21818240 is an apocalyptic number.

21818240 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 21818240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26493480).

21818240 is an abundant number, since it is smaller than the sum of its proper divisors (31168720).

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

21818240 is an equidigital number, since it uses as much as digits as its factorization.

21818240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 559 (or 547 counting only the distinct ones).

The product of its (nonzero) digits is 1024, while the sum is 26.

The square root of 21818240 is about 4670.9998929565. Note that the first 3 decimals coincide. The cubic root of 21818240 is about 279.4301334901.

The spelling of 21818240 in words is "twenty-one million, eight hundred eighteen thousand, two hundred forty".