20816640 has 216 divisors, whose sum is σ = 78121680. Its totient is φ = 5087232.

The previous prime is 20816623. The next prime is 20816659. The reversal of 20816640 is 4661802.

20816640 is a `hidden beast` number, since 2 + 0 + 8 + 16 + 640 = 666.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 149691 + ... + 149829.

Almost surely, 2^20816640 is an apocalyptic number.

20816640 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 20816640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39060840).

20816640 is an abundant number, since it is smaller than the sum of its proper divisors (57305040).

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

20816640 is a wasteful number, since it uses less digits than its factorization.

20816640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 179 (or 162 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 27.

The square root of 20816640 is about 4562.5256163664. The cubic root of 20816640 is about 275.0870908732.

The spelling of 20816640 in words is "twenty million, eight hundred sixteen thousand, six hundred forty".