20805840 has 240 divisors, whose sum is σ = 79387776. Its totient is φ = 4838400.

The previous prime is 20805791. The next prime is 20805853. The reversal of 20805840 is 4850802.

20805840 is a `hidden beast` number, since 2 + 0 + 80 + 584 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (240).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 293005 + ... + 293075.

Almost surely, 2^20805840 is an apocalyptic number.

20805840 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 20805840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39693888).

20805840 is an abundant number, since it is smaller than the sum of its proper divisors (58581936).

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

20805840 is a wasteful number, since it uses less digits than its factorization.

20805840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 138 (or 129 counting only the distinct ones).

The product of its (nonzero) digits is 2560, while the sum is 27.

The square root of 20805840 is about 4561.3419078162. The cubic root of 20805840 is about 275.0395094749.

The spelling of 20805840 in words is "twenty million, eight hundred five thousand, eight hundred forty".