21081808 has 20 divisors (see below), whose sum is σ = 44559648. Its totient is φ = 9582560.

The previous prime is 21081793. The next prime is 21081833. The reversal of 21081808 is 80818012.

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 3 ways as a sum of consecutive naturals, for example, 59716 + ... + 60067.

Almost surely, 2^21081808 is an apocalyptic number.

It is an amenable number.

21081808 is an abundant number, since it is smaller than the sum of its proper divisors (23477840).

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

21081808 is a wasteful number, since it uses less digits than its factorization.

21081808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 119802 (or 119796 counting only the distinct ones).

The product of its (nonzero) digits is 1024, while the sum is 28.

The square root of 21081808 is about 4591.4930033705. The cubic root of 21081808 is about 276.2502106835.

It can be divided in two parts, 2108 and 1808, that added together give a triangular number (3916 = T₈₈).

The spelling of 21081808 in words is "twenty-one million, eighty-one thousand, eight hundred eight".