21808518 has 24 divisors (see below), whose sum is σ = 46337352. Its totient is φ = 6841344.

The previous prime is 21808489. The next prime is 21808519. The reversal of 21808518 is 81580812.

It is a super-2 number, since 2×21808518² = 951222914712648, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21808519) by changing a digit.

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 11 ways as a sum of consecutive naturals, for example, 4555 + ... + 8022.

It is an arithmetic number, because the mean of its divisors is an integer number (1930723).

Almost surely, 2^21808518 is an apocalyptic number.

21808518 is an abundant number, since it is smaller than the sum of its proper divisors (24528834).

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

21808518 is a wasteful number, since it uses less digits than its factorization.

21808518 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12616 (or 12599 counting only the distinct ones).

The product of its (nonzero) digits is 5120, while the sum is 33.

The square root of 21808518 is about 4669.9591004633. The cubic root of 21808518 is about 279.3886235217.

The spelling of 21808518 in words is "twenty-one million, eight hundred eight thousand, five hundred eighteen".