20817985 has 4 divisors (see below), whose sum is σ = 24981588. Its totient is φ = 16654384.

The previous prime is 20817983. The next prime is 20817991. The reversal of 20817985 is 58971802.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 58971802 = 2 ⋅29485901.

It can be written as a sum of positive squares in 2 ways, for example, as 2362369 + 18455616 = 1537^2 + 4296^2 .

It is a cyclic number.

It is not a de Polignac number, because 20817985 - 2¹ = 20817983 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20817983) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2081794 + ... + 2081803.

It is an arithmetic number, because the mean of its divisors is an integer number (6245397).

Almost surely, 2^20817985 is an apocalyptic number.

It is an amenable number.

20817985 is a deficient number, since it is larger than the sum of its proper divisors (4163603).

20817985 is an equidigital number, since it uses as much as digits as its factorization.

20817985 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4163602.

The product of its (nonzero) digits is 40320, while the sum is 40.

The square root of 20817985 is about 4562.6730104183. The cubic root of 20817985 is about 275.0930153671.

The spelling of 20817985 in words is "twenty million, eight hundred seventeen thousand, nine hundred eighty-five".