20921840 has 20 divisors (see below), whose sum is σ = 48643464. Its totient is φ = 8368704.

The previous prime is 20921839. The next prime is 20921843. The reversal of 20921840 is 4812902.

It is a tau number, because it is divible by the number of its divisors (20).

It is a hoax number, since the sum of its digits (26) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20921843) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 130682 + ... + 130841.

Almost surely, 2^20921840 is an apocalyptic number.

20921840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20921840 is an abundant number, since it is smaller than the sum of its proper divisors (27721624).

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

20921840 is a wasteful number, since it uses less digits than its factorization.

20921840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 261536 (or 261530 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 26.

The square root of 20921840 is about 4574.0397899450. The cubic root of 20921840 is about 275.5497103435.

The spelling of 20921840 in words is "twenty million, nine hundred twenty-one thousand, eight hundred forty".