20815440 has 80 divisors (see below), whose sum is σ = 66061248. Its totient is φ = 5419008.

The previous prime is 20815343. The next prime is 20815441. The reversal of 20815440 is 4451802.

It is a tau number, because it is divible by the number of its divisors (80).

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 20815440.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20815441) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 9312 + ... + 11328.

Almost surely, 2^20815440 is an apocalyptic number.

20815440 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 20815440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33030624).

20815440 is an abundant number, since it is smaller than the sum of its proper divisors (45245808).

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

20815440 is a wasteful number, since it uses less digits than its factorization.

20815440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2076 (or 2070 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 24.

The square root of 20815440 is about 4562.3941083602. The cubic root of 20815440 is about 275.0818048640.

The spelling of 20815440 in words is "twenty million, eight hundred fifteen thousand, four hundred forty".