21808340 has 24 divisors (see below), whose sum is σ = 45942120. Its totient is φ = 8695808.

The previous prime is 21808337. The next prime is 21808349. The reversal of 21808340 is 4380812.

It can be written as a sum of positive squares in 4 ways, for example, as 5438224 + 16370116 = 2332^2 + 4046^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21808349) 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 7 ways as a sum of consecutive naturals, for example, 5516 + ... + 8604.

It is an arithmetic number, because the mean of its divisors is an integer number (1914255).

Almost surely, 2^21808340 is an apocalyptic number.

21808340 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21808340 is an abundant number, since it is smaller than the sum of its proper divisors (24133780).

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

21808340 is a wasteful number, since it uses less digits than its factorization.

21808340 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3451 (or 3449 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 26.

The square root of 21808340 is about 4669.9400424417. The cubic root of 21808340 is about 279.3878634012.

The spelling of 21808340 in words is "twenty-one million, eight hundred eight thousand, three hundred forty".