20665840 has 80 divisors (see below), whose sum is σ = 53496576. Its totient is φ = 7372800.

The previous prime is 20665837. The next prime is 20665849. The reversal of 20665840 is 4856602.

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 (31).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20665849) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 31920 + ... + 32560.

It is a vampire number, since it can be written as 2564 ⋅ 8060 (with its own digits).

Almost surely, 2^20665840 is an apocalyptic number.

20665840 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 20665840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26748288).

20665840 is an abundant number, since it is smaller than the sum of its proper divisors (32830736).

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

20665840 is a wasteful number, since it uses less digits than its factorization.

20665840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 698 (or 692 counting only the distinct ones).

The product of its (nonzero) digits is 11520, while the sum is 31.

The square root of 20665840 is about 4545.9696435414. The cubic root of 20665840 is about 274.4212179758.

The spelling of 20665840 in words is "twenty million, six hundred sixty-five thousand, eight hundred forty".