20421840 has 40 divisors (see below), whose sum is σ = 63308448. Its totient is φ = 5445760.

The previous prime is 20421803. The next prime is 20421859. The reversal of 20421840 is 4812402.

It is a tau number, because it is divible by the number of its divisors (40).

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 7 ways as a sum of consecutive naturals, for example, 42306 + ... + 42785.

Almost surely, 2^20421840 is an apocalyptic number.

20421840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20421840 is an abundant number, since it is smaller than the sum of its proper divisors (42886608).

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

20421840 is a wasteful number, since it uses less digits than its factorization.

20421840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 85107 (or 85101 counting only the distinct ones).

The product of its (nonzero) digits is 512, while the sum is 21.

The square root of 20421840 is about 4519.0529981402. The cubic root of 20421840 is about 273.3369158100.

The spelling of 20421840 in words is "twenty million, four hundred twenty-one thousand, eight hundred forty".