20505840 has 80 divisors (see below), whose sum is σ = 65079168. Its totient is φ = 5338368.

The previous prime is 20505839. The next prime is 20505841. The reversal of 20505840 is 4850502.

It is an interprime number because it is at equal distance from previous prime (20505839) and next prime (20505841).

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 20505840.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20505841) 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, 9327 + ... + 11313.

Almost surely, 2^20505840 is an apocalyptic number.

20505840 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 20505840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32539584).

20505840 is an abundant number, since it is smaller than the sum of its proper divisors (44573328).

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

20505840 is a wasteful number, since it uses less digits than its factorization.

20505840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2046 (or 2040 counting only the distinct ones).

The product of its (nonzero) digits is 1600, while the sum is 24.

The square root of 20505840 is about 4528.3374432566. The cubic root of 20505840 is about 273.7111702395.

The spelling of 20505840 in words is "twenty million, five hundred five thousand, eight hundred forty".