20856640 has 56 divisors (see below), whose sum is σ = 56765952. Its totient is φ = 7150080.

The previous prime is 20856629. The next prime is 20856679. The reversal of 20856640 is 4665802.

It is a tau number, because it is divible by the number of its divisors (56).

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, 2416 + ... + 6895.

Almost surely, 2^20856640 is an apocalyptic number.

20856640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20856640 is an abundant number, since it is smaller than the sum of its proper divisors (35909312).

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

20856640 is an equidigital number, since it uses as much as digits as its factorization.

20856640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9335 (or 9325 counting only the distinct ones).

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

The square root of 20856640 is about 4566.9070496344. The cubic root of 20856640 is about 275.2631750583.

The spelling of 20856640 in words is "twenty million, eight hundred fifty-six thousand, six hundred forty".